Fix automatic brightness

Broken in Iddcbee98f6588bba428c4059e786d946d7ce2298

- Brightness is now handled in handleLightSensorValue instead of
  onSensorChanged, but the previous patch copied the old handling
  code into onSensorChanged in addition to calling handleLightSensorValue.
  This patch integrates the brightness filter change from
  onSensorChanged into handleLightSensorValue.
- onSensorChanged called mHandler.removeCallbacks(mAutoBrightnessTask)
  every time a value is received from the sensor ensuring that the
  task never get ran! (We schedule it 2 seconds into the future
  but receives a value from the sensor every second.)
  This patch removes the call.

(Note: similar to http://review.cyanogenmod.com/11341)

Change-Id: Id3e4f0f02f91f27c7c12cb2e274e0c13213d4774