Remove PowerManager.setAutoBrightness()

We will use the System.SCREEN_BRIGHTNESS_MODE Settings value instead.
Add SCREEN_BRIGHTNESS_MODE_MANUAL and SCREEN_BRIGHTNESS_MODE_AUTOMATIC constants.

Change-Id: I01935be3fcb48cf76392d2c594205cb47babc5b2
Signed-off-by: Mike Lockwood <lockwood@android.com>