SystemUI: clean up tuner

- Remove preferences we handle elsewhere (battery)
- Remove link to QSTuner
- Separate out statusbar icon prefs into separate preferences so we can
  launch it externally

Change-Id: Icc01b443dab945374a0df19a4f0359e3df4ea7d9
Signed-off-by: Roman Birg <roman@cyngn.com>