clutter/stage: Remove 'minimum window size' logic

It was a feature relevant for when Clutter was an application toolkit
that wanted the application window to communicate a minimum size to the
windowing system.

Now, clutter is part of the windowing system component, so this feature
doesn't make any sense, so remove it.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2002>

src/tests/clutter/interactive/test-stage-sizing.c

@@ -71,10 +71,6 @@ test_stage_sizing_main (int argc, char *argv[])
   clutter_actor_add_child (rect, label);
   clutter_actor_add_child (box, rect);
 
-  clutter_stage_set_minimum_size (CLUTTER_STAGE (stage),
-                                  clutter_actor_get_width (box),
-                                  clutter_actor_get_height (box));
-
   clutter_actor_show (stage);
 
   clutter_test_main ();