A better solution for ignoring user activity while the screen is animating off.

Fixes a deadlock that occurred because mAnimatingScreenOff was left set to true
after aborting turning off the screen.
This change removes the mAnimatingScreenOff flag and checks for
(mScreenBrightness.animating && mScreenBrightness.targetValue == 0) instead.

Fixes bug b/2219706

Change-Id: I081f08c14ad7585a953fb567867238b1f3db841f
Signed-off-by: Mike Lockwood <lockwood@android.com>