Settings: defer DEV_FORCE_SHOW_NAVBAR query to CMSettings

Some apps were using Settings.System.DEV_FORCE_SHOW_NAVBAR to determine
whether the device was forcing a nav bar. It was then moved to
Settings.Secure, and then to CMSettings.Secure.

So some apps check against Settings.System, and some may check against
Settings.Secure. The real value lives in CMSettings.Secure right now.

We could not intercept the setting because MOVED_TO_SECURE would return
the already-cached value from Settings.Secure, not allowing us to
intercept the call in CMSettings.

With this removal, we can handle the logic for this key in
CMSettingsProvider.

Ticket: CYNGNOS-2480

Change-Id: I7485c0d0acf90df365e5ed5ebdb42596d148de62
Signed-off-by: Roman Birg <roman@cyngn.com>
(cherry picked from commit adbe5616)