libyang CHANGE unify the statement enumerations

Instead of keeping a separate enumeration for YANG extension pattern
statements, just use the standard ly_stmt enumeration.
diff --git a/src/tree_schema.c b/src/tree_schema.c
index b64665c..4377cfd 100644
--- a/src/tree_schema.c
+++ b/src/tree_schema.c
@@ -999,7 +999,7 @@
     ext_p->format = LY_PREF_SCHEMA;
     ext_p->prefix_data = mod;
     ext_p->flags = LYS_INTERNAL;
-    ext_p->insubstmt = LYEXT_SUBSTMT_SELF;
+    ext_p->insubstmt = LY_STMT_NONE;
     ext_p->insubstmt_index = 0;
 
     ext_p->child = stmt = calloc(1, sizeof *ext_p->child);
@@ -1065,7 +1065,7 @@
     ext_p->format = LY_PREF_SCHEMA;
     ext_p->prefix_data = mod;
     ext_p->flags = LYS_INTERNAL;
-    ext_p->insubstmt = LYEXT_SUBSTMT_SELF;
+    ext_p->insubstmt = LY_STMT_NONE;
     ext_p->insubstmt_index = 0;
 
     ext_p->child = stmt = calloc(1, sizeof *ext_p->child);
@@ -1116,7 +1116,7 @@
     ext_p->format = LY_PREF_SCHEMA;
     ext_p->prefix_data = mod;
     ext_p->flags = LYS_INTERNAL;
-    ext_p->insubstmt = LYEXT_SUBSTMT_SELF;
+    ext_p->insubstmt = LY_STMT_NONE;
     ext_p->insubstmt_index = 0;
 
     ext_p->child = stmt = calloc(1, sizeof *ext_p->child);
@@ -1167,7 +1167,7 @@
     ext_p->format = LY_PREF_SCHEMA;
     ext_p->prefix_data = mod;
     ext_p->flags = LYS_INTERNAL;
-    ext_p->insubstmt = LYEXT_SUBSTMT_SELF;
+    ext_p->insubstmt = LY_STMT_NONE;
     ext_p->insubstmt_index = 0;
 
     ext_p->child = stmt = calloc(1, sizeof *ext_p->child);