DO NOT MERGE Fix bug in getCurrentLocation cancellation

Cancellation was not being propagated to the system server due to a
misunderstanding on how CancellationSignal functions. There is no
noticable impact for the user, as cancellation did properly prevent any
further locations, however this would have resulted in extra
power draw since the system server would not have canceled the
associated provider location request. This would have left
getCurrentLocation() as equivalent to requestSingleUpdate() where it was
supposed to be an all-around improvement that could save power.

Bug: 168666216
Test: manual + presubmits
Change-Id: I5c77db4cc56cce1b984587f65d2bcfb488436bb8