settings: Move headset option, hide MoreDeviceSettings if empty

 * This option fits much better in the sound menu under "automation
   and effects", and on many devices it's the only option in the
   "More..." menu under Tap & Pay.
 * Move it, and remove the MoreDeviceSettings top-level category if
   there's nothing else in it.

Change-Id: I83e88d8941149a8d3443ef95991b4e5ec3c4db86
Merge "settings: Move headset option, hide MoreDeviceSettings if empty" into pac-4.4