This API has been broken for quite some time now as the corresponding
mutter function meta_monitor_manager_get_monitor_for_output was removed.
If anyone tries to use it, we would just run into a backtrace.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/490
While it is possible to register accelerators in-bulk, there is no
proper way to unregister them again. This adds the corresponding call
for UngrabAccelerator to allow ungrabbing multiple accelerators at the
same time.
The idea is that g-s-d can use this in the future to simplify the
keybinding reload logic.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/429
