Settings: remove Expanded Desktop from Power Menu if unavailable

Instead of disabling the option when it is disabled, let's remove the
Expanded Desktop option in Power Menu Settings.

When the user toggles Expanded Desktop to ON, it will automatically add
the option to the power menu. The user can then remove it if they wish,
and all the states are properly kept.

Change-Id: I23b6a44da86c1cd74e3f73a8edc714ceeb47af4d
Signed-off-by: Roman Birg <roman@cyngn.com>