wayland: Implement registry remove handler

wayland: Implement registry remove handler

Wayland event handlers are never optional. libwayland-client will abort
the program if events for unbound handlers are to be dispatched.
Although the event queue is only dispatched a few times during
initialization for getting the wl_drm global and authenticating the DRM
device, in rare circumstances it can happen that another global such as
a wl_output - or even wl_drm itself - is removed during that time, which
would crash the program. Implement the handler to fix this.

Fixes: #99

Signed-off-by: Philipp Kerling <pkerling@casix.org>