MAINTENANCE correct license text in source codes

THIS DOES NOT CHANGE THE LICENSE!

We had an incomplete text of BSD 3-Clause license in source codes.
So now the License text is stored in LICENSE file and the text in
source codes just refers to the full text of BSD 3-Clause License.
diff --git a/tests/config.h.in b/tests/config.h.in
index c026018..e6f76b3 100644
--- a/tests/config.h.in
+++ b/tests/config.h.in
@@ -5,18 +5,11 @@
  *
  * Copyright (c) 2015 CESNET, z.s.p.o.
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- * 3. Neither the name of the Company nor the names of its contributors
- *    may be used to endorse or promote products derived from this
- *    software without specific prior written permission.
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     https://opensource.org/licenses/BSD-3-Clause
  */
 
 #define TESTS_DIR "@CMAKE_SOURCE_DIR@/tests/"
diff --git a/tests/test_fd_comm.c b/tests/test_fd_comm.c
index ec6f16b..79a1fb8 100644
--- a/tests/test_fd_comm.c
+++ b/tests/test_fd_comm.c
@@ -5,19 +5,11 @@
  *
  * Copyright (c) 2015 CESNET, z.s.p.o.
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- * 3. Neither the name of the Company nor the names of its contributors
- *    may be used to endorse or promote products derived from this
- *    software without specific prior written permission.
- *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     https://opensource.org/licenses/BSD-3-Clause
  */
 
 #include <errno.h>
diff --git a/tests/test_init_destroy_ssh.c b/tests/test_init_destroy_ssh.c
index c91600a..5c9a7a3 100644
--- a/tests/test_init_destroy_ssh.c
+++ b/tests/test_init_destroy_ssh.c
@@ -5,19 +5,11 @@
  *
  * Copyright (c) 2015 CESNET, z.s.p.o.
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- * 3. Neither the name of the Company nor the names of its contributors
- *    may be used to endorse or promote products derived from this
- *    software without specific prior written permission.
- *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     https://opensource.org/licenses/BSD-3-Clause
  */
 
 #include <errno.h>
diff --git a/tests/test_init_destroy_ssh_tls.c b/tests/test_init_destroy_ssh_tls.c
index d492740..eb39d06 100644
--- a/tests/test_init_destroy_ssh_tls.c
+++ b/tests/test_init_destroy_ssh_tls.c
@@ -5,19 +5,11 @@
  *
  * Copyright (c) 2015 CESNET, z.s.p.o.
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- * 3. Neither the name of the Company nor the names of its contributors
- *    may be used to endorse or promote products derived from this
- *    software without specific prior written permission.
- *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     https://opensource.org/licenses/BSD-3-Clause
  */
 
 #include <errno.h>
diff --git a/tests/test_init_destroy_tls.c b/tests/test_init_destroy_tls.c
index 13601fe..93ce74f 100644
--- a/tests/test_init_destroy_tls.c
+++ b/tests/test_init_destroy_tls.c
@@ -5,19 +5,11 @@
  *
  * Copyright (c) 2015 CESNET, z.s.p.o.
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- * 3. Neither the name of the Company nor the names of its contributors
- *    may be used to endorse or promote products derived from this
- *    software without specific prior written permission.
- *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     https://opensource.org/licenses/BSD-3-Clause
  */
 
 #include <errno.h>
diff --git a/tests/test_io.c b/tests/test_io.c
index d8d5890..6b08f42 100644
--- a/tests/test_io.c
+++ b/tests/test_io.c
@@ -5,19 +5,11 @@
  *
  * Copyright (c) 2015 CESNET, z.s.p.o.
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- * 3. Neither the name of the Company nor the names of its contributors
- *    may be used to endorse or promote products derived from this
- *    software without specific prior written permission.
- *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     https://opensource.org/licenses/BSD-3-Clause
  */
 
 #include <errno.h>
diff --git a/tests/test_server_thread.c b/tests/test_server_thread.c
index f1a775e..17e702f 100644
--- a/tests/test_server_thread.c
+++ b/tests/test_server_thread.c
@@ -5,19 +5,11 @@
  *
  * Copyright (c) 2015 CESNET, z.s.p.o.
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- * 3. Neither the name of the Company nor the names of its contributors
- *    may be used to endorse or promote products derived from this
- *    software without specific prior written permission.
- *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     https://opensource.org/licenses/BSD-3-Clause
  */
 
 #include <pthread.h>