With the old screen shield, we were simply hiding the lightboxes to show
the shield when the user became active after activating the shield but
before locking the screen (that is, when using a lock-delay).
However now that the shield is gone, we end up showing the unlock dialog
even though we are not actually locked.
We probably don't want to add back a shield-like mode (that is, a way to
raise the unlock dialog without authentication when we aren't locked),
so just deactivate the whole shield when the user becomes active again
before the lock kicks in.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/2213
6f12864776