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/tests/utests/data/test_tree_data.c b/tests/utests/data/test_tree_data.c
index 91b0738..38a7239 100644
--- a/tests/utests/data/test_tree_data.c
+++ b/tests/utests/data/test_tree_data.c
@@ -296,7 +296,7 @@
     assert_int_equal(LY_SUCCESS, ly_path_parse(ctx, NULL, path_str, strlen(path_str), LY_PATH_BEGIN_EITHER, LY_PATH_LREF_FALSE,
                                                LY_PATH_PREFIX_OPTIONAL, LY_PATH_PRED_SIMPLE, &exp));
     assert_int_equal(LY_SUCCESS, ly_path_compile(ctx, NULL, NULL, exp, LY_PATH_LREF_FALSE, LY_PATH_OPER_INPUT,
-                                                 LY_PATH_TARGET_SINGLE, lydjson_resolve_prefix, NULL, LYD_JSON, &path));
+                                                 LY_PATH_TARGET_SINGLE, LY_PREF_JSON, NULL, &path));
     term = lyd_target(path, tree);
 
     assert_string_equal(term->schema->name, "d");