Remove checks for GLSL

The Cogl feature was removed a while back, while Clutter just hard coded
it to TRUE. Lets remove the confusion that GLSL isn't supported and just
remove the (dead) fallback paths.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2015>

src/tests/clutter/conform/actor-pick.c

@@ -92,9 +92,6 @@ on_timeout (gpointer data)
         }
       else if (test_num == 3)
         {
-          if (!clutter_feature_available (CLUTTER_FEATURE_SHADERS_GLSL))
-            continue;
-
           clutter_actor_hide (over_actor);
 
           clutter_actor_add_effect_with_name (CLUTTER_ACTOR (state->stage),

src/tests/clutter/conform/actor-shader-effect.c

@@ -259,9 +259,6 @@ actor_shader_effect (void)
   gboolean was_painted;
   GList *actors = NULL;
 
-  if (!clutter_feature_available (CLUTTER_FEATURE_SHADERS_GLSL))
-    return;
-
   stage = clutter_test_get_stage ();
 
   rect = make_actor (foo_old_shader_effect_get_type ());