bug#36924: GDM, GNOME Shell, etc. break when there are stale caches

[reyman via web]

Hi there
After removing `gdm login` using a transformer and forget to modify/amend it 
into build-custom-services i break my system : 

(define-public %dm/system-services
  (append (build-custom-services identity)
            (modify-services %desktop-services
            (delete gdm-service-type))))

My gnome crash, and when i even when i try to roll-back, it was impossible to 
login, my screen freeze at login/password, just before gnome start.

Error in message : 

ul  4 17:44:11 localhost elogind[427]: New session c1 of user gdm.
Jul  4 17:44:11 localhost gdm-session-worker: GLib-GObject: g_object_unref: 
assertion 'G_IS_OBJECT (object)' failed 
Jul  4 17:44:11 localhost gdm: Gdm: GdmDisplay: Session never registered, 
failing 
Jul  4 17:44:11 localhost elogind[427]: Removed session c1.
Jul  4 17:44:11 localhost gdm: Gdm: Child process -552 was already dead. 
Jul  4 17:44:11 localhost gdm: Gdm: GdmDisplay: Session never registered, 
failing 
Jul  4 17:44:11 localhost gdm: Gdm: Child process -552 was already dead. 

Removing /var/lib/gdm and mkdir gdm, rebooting with rollback solving the 
problem. 

during a guix system reconfigure