tests/clutter: Always use stage from backend

This removes all occurrences of creating a custom stage from the tests,
making them always use the one from MetaBackend. This will allow for
further cleanups.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1364

src/tests/clutter-test-utils.h

@@ -86,8 +86,6 @@ G_BEGIN_DECLS
 int \
 main (int argc, char *argv[]) \
 { \
-  meta_test_init ();\
-\
   clutter_test_init (&argc, &argv); \
 \
   { \
@@ -100,9 +98,23 @@ main (int argc, char *argv[]) \
 CLUTTER_EXPORT
 void            clutter_test_init               (int            *argc,
                                                  char         ***argv);
+
+CLUTTER_EXPORT
+void            clutter_test_init_with_args     (int            *argc,
+                                                 char         ***argv,
+                                                 const char     *parameter_string,
+                                                 GOptionEntry   *entries,
+                                                 const char     *translation_domain);
+
 CLUTTER_EXPORT
 int             clutter_test_run                (void);
 
+CLUTTER_EXPORT
+void            clutter_test_main               (void);
+
+CLUTTER_EXPORT
+void            clutter_test_quit               (void);
+
 CLUTTER_EXPORT
 void            clutter_test_add                (const char     *test_path,
                                                  GTestFunc       test_func);