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: Idd82f582a1ba54f8b45fbd4fbe631057e9515f86
[2/2] Battery light: Add 100% charged level
[2/2] Profile: Screen timeout
[2/2] Buttons: Switch to last app
[2/2] Quick pulldown: center
[2/2] Smart pulldown
[2/2] Volume panel timeout
[2/2] Low battery warning policy
[2/2] Recents clear all button
[2/2] Recents RAM bar
[2/2] Network traffic indicator
[2/2] Lockscreen notifications