We haven't supported disabling stage views in the native backend since
commit 70edc7dda48b57ead25f159243ee131e99bd7956
Author: Jonas Ådahl <jadahl@gmail.com>
Date: Mon Jul 24 12:31:32 2017 +0800
backends/native: Stop supporting stage views being disabled
There were still some left over checks; lets remove them.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/343