Fix automatic brightness when filtering is disabled

(Broke in I9c88704484f4a23b3d643597f35b55d74cf36b56)

- Do not mHandler.removeCallbacks(mAutoBrightnessTask) every time
  a value is received from the sensor because that will ensure that
  the task ever get ran! (We schedule it 2 seconds into the future
  but receives a value from the sensor every second.)
- Replace the algorithm for brightness change (non-filtering) with
  the original algorithm before the patch. (Not sure why the patch
  changed it.)

Change-Id: I71f6f23c53974fbb763d46ea4023623d2bbeb250