don't pin ranking updates at the end of the queue.

Apparently we schedule ranking updates all the time, so the job gets pulled
to the end of the queue, and can get starved. This change makes sure we
don't schedule multiple updates by leaving it in the queue. If a job in the
queue behind hte update request needs to send an update it will jsut
request one anyway, so we shouldn't miss updates.

Bug: 28015158
Change-Id: Id5b9d05ea6eb35e610ee34651e4cde8cddd4ae66