AodPolicy: Fix service leak

Fixes an issue where the AlwaysOnDisplayPolicy leaked a service
context, and with it the entirety of DozeMachine, preventing
wakelocks from being GCed and preventing them from being
fallback-released.

Bug: 78402666
Test: Toggle screen on and off a few times, verify that DozeService is not being leaked.
Change-Id: Ie3ad67c2d0c83760f4d04a53394fab4a3a35d6bc