community/mutter: drop zenity dependency
mutter no longer depends on zenity as of version 43.alpha.
See https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2370 And https://gitlab.gnome.org/GNOME/mutter/-/blob/e331e38a191a36faaa5bb049157ab77f94fd7654/NEWS#L137
Do you think this looks fine @pabloyoyoista?