* Removed obsolete code.
* Callback call isn't inside synchronize now.
* A request could be sent twice.

After purging expired requests, the following was possible:
1. A new request of 0.5 second is queued and sent to SleeperNotifier. Thus,
   becoming #1 in queue.
2. After-purging code looking to send something to SleeperNotifier would send it
   again.