Fix bug of unnecessary wakeups after completed syncs.

Cancel unnecessary wakeup alarms for completed syncs for power savings.  SyncManager scheduled a 5 min wakeup alarm for timing out long running syncs.  These remained even when the sync completes before the timeout.  This removes the alarm when the sync finishes; results in a ~50% decrease in wakeups due to sync.

Change-Id: I163c5a99aae354d7df7297a6e7738b0ff8a655df