schema CHANGE remove LYEXT_PARENT duplicating ly_stmt

Removing the enumeration also leads to simplify the extension instance
structure where was the information about the parent structure duplicated.
diff --git a/src/plugins_exts_nacm.c b/src/plugins_exts_nacm.c
index 460ca75..7674002 100644
--- a/src/plugins_exts_nacm.c
+++ b/src/plugins_exts_nacm.c
@@ -55,7 +55,7 @@
 
         inherited->def = lysc_ext_dup(arg->c_ext->def);
         inherited->parent = node;
-        inherited->parent_type = LYEXT_PAR_NODE;
+        inherited->parent_stmt = lys_nodetype2stmt(node->nodetype);
         if (arg->c_ext->argument) {
             LY_CHECK_RET(lydict_insert(node->module->ctx, arg->c_ext->argument, strlen(arg->c_ext->argument),
                     &inherited->argument));
@@ -92,9 +92,9 @@
     }
 
     /* check that the extension is instantiated at an allowed place - data node */
-    if (c_ext->parent_type != LYEXT_PAR_NODE) {
+    if (!LY_STMT_IS_NODE(c_ext->parent_stmt)) {
         lyext_log(c_ext, LY_LLWRN, 0, cctx->path, "Extension %s is allowed only in a data nodes, but it is placed in \"%s\" statement.",
-                p_ext->name, lyext_parent2str(c_ext->parent_type));
+                p_ext->name, ly_stmt2str(c_ext->parent_stmt));
         return LY_ENOT;
     } else {
         parent = (struct lysc_node *)c_ext->parent;