Fix finishOp for HotwordDetectionService

We currently specially handle the HotwordDetectionService uid in
AppOpsPolicy. But CheckOpsDelegate doesn't currently include finishOp,
so that doesn't work for the hotword service. This change adds finishOp
to the interface and implements it in AppOpsPolicy to be consistent with
the other ops.

Bug: 190011174
Test: manual - no error in logs for finishOp
Test: manual - privacy indicator works as expected (with another wip
 change)
Change-Id: I77907092a917362aacd0d5562e54abd6f3c3d47b