libyang REFACTOR prefix format always decides the callback (#1169)

So the callback is no longer needed as a parameter.
Also, union no longer uses its own prefix mappings
but instead uses the original format and copies any
required prefix data.
diff --git a/src/context.c b/src/context.c
index bb7a432..e7b4773 100644
--- a/src/context.c
+++ b/src/context.c
@@ -560,7 +560,7 @@
     /* compile */
     oper = output ? LY_PATH_OPER_OUTPUT : LY_PATH_OPER_INPUT;
     ret = ly_path_compile(ctx, NULL, ctx_node, exp, LY_PATH_LREF_FALSE, oper, LY_PATH_TARGET_MANY,
-                          lydjson_resolve_prefix, NULL, LYD_JSON, &p);
+                          LY_PREF_JSON, NULL, &p);
     LY_CHECK_GOTO(ret, cleanup);
 
     /* get last node */