Fix adb shell command for screen_brightness

This was caused by ag/10665448 removing BrightnessSynchronizer from
DisplayPowerController.

Bug: 153744973

Test: atest android.cts.statsd.atom.UidAtomTests#testScreenBrightness
Manual, check brightness changes accordingly:
adb shell settings put system screen_brightness_float 0.9
adb shell settings put system screen_brightness 2

Change-Id: I86c80ae1aa1d34d9221a09da11a48f9845506bea