title: How does NotificationHub remove the registration devices
body: <p>In the diagnostic console in visual studio under the Azure->NotificationHub, after I registered my device to the hub, the expiration date shown is 9999 years by default. If I removed my application, the registration still exist. Later I re-install the application, a new creation of the registration added to the list. The old registration never get deleted. </p>
  
  <p>Do I have to manually set an expiration date? It sounds not logical, coz the application still using it. How can the Notification Hub delete the old registered devices when the application was uninstalled.</p>