Don't show sensor use dialog for system uid

If the system uid is being noted for mic or camera op, it will have to
be explicitely accounted for to show the user any sort of UI to unmute
the mic or camera.

Test: Add some logcat statements to verify the correct code paths are
          being hit when placing and answering phone calls and when
	  trying to trigger hotword.
Bug: 195122900
Change-Id: I601458ea2dd7557e4a557eab32c2da15828ae4a7