Ensure that DozeSensors can unregister itself.

When DozeService shuts down, we need to ensure that any registered
callbacks in DozeSensors get a chance to remove themselves from the
SensorManager.

Fixes: 155104806
Test: atest SystemUITests
Change-Id: I5126cdb1b65d4db42674722839adb7331091e099
5 files changed