Ensure stale updates only happen while stale

Remove condition where a non-stale liveData would fully update itself if
all of its sources were not stale, even if the liveData itself was
already not stale. Also replaced job cancellation with a job queue. If
multiple async jobs wish to run for one async LiveData, the LiveData
will update once, once the current job is finished.

Fixes: 147473081
Test: Rapidly click between the "Location" and Settings home page
screens. The number of location apps should not change.

Change-Id: I65a74c8ce5c0c0bcbf51674146505f7601d76e64