wayland-winsys: Provide a wl_registry.global_remove callback
wayland-winsys: Provide a wl_registry.global_remove callback

Otherwise libwayland-client will abort() when we get that event.

https://bugzilla.gnome.org/show_bug.cgi?id=743594

djdeath/cogl,djdeath/cogl,djdeath/cogl