glx: Remove unused Atom members from ClutterBackendGLX
glx: Remove unused Atom members from ClutterBackendGLX

The atoms were moved to the shared X11 backend structure ages ago.

collects/clutter,ebassi/clutter,jigpu/clutter,ebassi/clutter,djdeath/clutter,heysion/clutter-clone,kerrickstaley/clutter-vala,collects/clutter,collects/clutter,spatulasnout/clutter,djdeath/clutter-multithreaded,Distrotech/clutter,GNOME/clutter,GNOME/clutter,kerrickstaley/clutter-vala,jigpu/clutter,djdeath/clutter-android,Distrotech/clutter,ebassi/clutter,Distrotech/clutter,collects/clutter,GNOME/clutter,GNOME/clutter,jigpu/clutter,kerrickstaley/clutter-vala,djdeath/clutter-multithreaded,GNOME/clutter,heysion/clutter-clone,spatulasnout/clutter,djdeath/clutter,djdeath/clutter,djdeath/clutter,heysion/clutter-clone,Distrotech/clutter,Distrotech/clutter,jigpu/clutter,spatulasnout/clutter,spatulasnout/clutter,djdeath/clutter-multithreaded,heysion/clutter-clone,jigpu/clutter,Distrotech/clutter,ebassi/clutter,djdeath/clutter-android,jigpu/clutter,spatulasnout/clutter,heysion/clutter-clone,djdeath/clutter,djdeath/clutter,ebassi/clutter,djdeath/clutter-multithreaded,djdeath/clutter-android,djdeath/clutter-android,djdeath/clutter-android,kerrickstaley/clutter-vala,collects/clutter