Apply "most-recent" delivery policy to ACTION_USER_RESTRICTIONS_CHANGED.

This allows us to skip any older ACTION_USER_RESTRICTIONS_CHANGED
broadcasts waiting to be delivered when a new broadcast is dispatched.
It should be safe to discard the older ones as the broadcast is only
indicating that something has changed.

Bug: 265079364
Test: atest tests/devicepolicy/src/android/devicepolicy/cts/UserRestrictionsTest.java
Test: atest hostsidetests/devicepolicy/src/com/android/cts/devicepolicy/UserRestrictionsTest.java
Change-Id: I97c7495f13520b5c8a894b76343deae20d1824e9