clutter/stage: Only emit "presented" on completion event

We'd emit multiple "presented" signals per frame, one for "sync" and one
for "completion". Only the latter were ever used, and removing the
differentiation eases the avoidance of cogl onscreen framebuffer frame
callback details leaking into clutter.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1285

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

@@ -7,7 +7,6 @@
 
 static void
 on_presented (ClutterStage     *stage,
-              CoglFrameEvent   *frame_event,
               ClutterFrameInfo *frame_info,
               gboolean         *was_presented)
 {