clutter: Drop unused API

clutter_stage_*_get_clip_region_bounds() is no longer used and may be
removed.

!867
5 jobs for !867 with wip/carlosg/clip-regions in 6 minutes and 28 seconds (queued for 3 seconds)
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Status Job ID Name Coverage
  Review
passed #507186
check-commit-log

00:00:21

 
  Build
passed #507187
build-mutter

00:03:28

passed #507188
build-without-native-backend-and-wayland

00:01:42

 
  Test
passed #507190
can-build-gnome-shell

00:01:11

passed #507189
test-mutter

00:02:38