Fix problem with proximity sensor not reawaking screen if the values change too quickly.

The logic that disables user activity while turning off the screen should not affect proximity sensor.

Fixes bug b/2228734 (in-call, prox sensor gets confused)

Change-Id: Ieca126e6f79bf7baa5741981aea72d306ba03edc
Signed-off-by: Mike Lockwood <lockwood@android.com>