schema CHANGE remove private_destructor parameter from ly_ctx_destroy()

The mechanism was not reliable and not used often. libyang provide
function to traverse the schema and free the set data manually or the
caller can maintain some information to free the set data directly.

This commit changes API.
diff --git a/tests/fuzz/buf_add_char.c b/tests/fuzz/buf_add_char.c
index 33ca222..0f472b8 100644
--- a/tests/fuzz/buf_add_char.c
+++ b/tests/fuzz/buf_add_char.c
@@ -46,7 +46,7 @@
 
 	free(old_data);
 	free(dest);
-	ly_ctx_destroy(ctx, NULL);
+	ly_ctx_destroy(ctx);
 
 	return 0;
 }
diff --git a/tests/fuzz/lyd_parse_mem_json.c b/tests/fuzz/lyd_parse_mem_json.c
index cd4be88..912dce6 100644
--- a/tests/fuzz/lyd_parse_mem_json.c
+++ b/tests/fuzz/lyd_parse_mem_json.c
@@ -75,7 +75,7 @@
 	data[len] = 0;
 
 	lyd_parse_data_mem(ctx, data, LYD_JSON, 0, LYD_VALIDATE_PRESENT, &tree);
-	ly_ctx_destroy(ctx, NULL);
+	ly_ctx_destroy(ctx);
 
 	free(data);
 
diff --git a/tests/fuzz/lyd_parse_mem_xml.c b/tests/fuzz/lyd_parse_mem_xml.c
index e85d84a..f835f7f 100644
--- a/tests/fuzz/lyd_parse_mem_xml.c
+++ b/tests/fuzz/lyd_parse_mem_xml.c
@@ -75,7 +75,7 @@
 	data[len] = 0;
 
 	lyd_parse_data_mem(ctx, data, LYD_XML, 0, LYD_VALIDATE_PRESENT, &tree);
-	ly_ctx_destroy(ctx, NULL);
+	ly_ctx_destroy(ctx);
 
 	free(data);
 
diff --git a/tests/fuzz/lys_parse_mem.c b/tests/fuzz/lys_parse_mem.c
index 59884f3..ea244d1 100644
--- a/tests/fuzz/lys_parse_mem.c
+++ b/tests/fuzz/lys_parse_mem.c
@@ -31,7 +31,7 @@
 	data[len] = 0;
 
 	lys_parse_mem(ctx, data, LYS_IN_YANG, NULL);
-	ly_ctx_destroy(ctx, NULL);
+	ly_ctx_destroy(ctx);
 	free(data);
 	return 0;
 }
diff --git a/tests/fuzz/yang_parse_module.c b/tests/fuzz/yang_parse_module.c
index c25a5d2..5c235a2 100644
--- a/tests/fuzz/yang_parse_module.c
+++ b/tests/fuzz/yang_parse_module.c
@@ -46,6 +46,6 @@
 
 	free(data);
 	free(mod);
-	ly_ctx_destroy(ctx, NULL);
+	ly_ctx_destroy(ctx);
 	return 0;
 }