Update gnome-settings-daemon plugins required in GDM session
This MR drops 3 daemons:
- gsd-clipboard
- gsd-mouse
- gsd-xsettings
The first 2 were dropped in g-s-d, as the functionality moved to mutter. The last one shouldn't be strictly needed by the other components of the GDM session and is an obstacle to making GDM use a Xwayland-less session.