actor: Use the TOPLEVEL flag instead of a type check
actor: Use the TOPLEVEL flag instead of a type check

We can use the internal private CLUTTER_ACTOR_IS_TOPLEVEL flag, which is
set only on Stages.

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