clients: add global_remove handler stubs

clients: add global_remove handler stubs

All the clients here were missing the global_remove handler. Because
window.c did not have it, weston-desktop-shell and weston-keyboard
segfaulted on compositor exit, as they received some
wl_registry.global_remove events.

Add more or less stub global_remove handlers, so that clients do not
crash on such events. Toytoolkit and all applications would need a lot
more code to properly handle the global object removal.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>