cogl: Remove some unused #define GL_BLAH safeties

None of these constants are referenced in the files defining them.

GNOME/mutter!1194
7 jobs for !1194 with cogl-driver-cleanup in 20 minutes and 33 seconds (queued for 4 seconds)
detached
Status Job ID Name Coverage
  Review
passed #773543
check-commit-log

00:01:50

 
  Build
passed #773544
build-mutter

00:10:18

passed #773546
build-without-native-backend-and-wayland

00:04:06

passed #773545
build-without-opengl-and-glx

00:04:24

 
  Test
passed #773548
can-build-gnome-shell

00:03:04

passed #773549
test-mutter

00:05:19

failed #773547
test-mutter

00:04:29