material: free any layer cache in material_set_parent
material: free any layer cache in material_set_parent

Previously in _cogl_material_pre_change_notify we manually freed the
layer caches of a material if we caused a reparent, but it makes more
sense to have _cogl_material_set_parent do this directly instead.

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