Adapt to pick changes

It turns out, StViewport's pick implementation was broken, since
Clutter stopped reading clipping from the framebuffer. Rejoice with
bugfixing by removing code!

!1470
8 jobs for !1470 with gbsneto/graphene-ray in 13 minutes and 27 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Review
passed #944630
check_commit_log

00:01:05

passed #944632
eslint

00:02:30

passed #944631
js_check

00:00:42

passed #944634
no_template_check

00:00:33

passed #944633
potfile_check

00:13:26

 
  Build
passed #944635
build

00:04:22

passed #944636
flatpak
flatpak

00:01:57

 
  Test
passed #944637
test

00:00:58