title: Firebase - Delete a device group without knowing the registration ids of its members
body: <p>While working with Firebase and Device Groups, I was testing the case in which the token (registration id) changes (for example after reinstalling the app) but my logic failed because after reinstalling the app i have no more way to know the previously stored token . </p>
  
  <p>The problem is that now I have a device group with two <code>"ghost"</code> registration ids that I don't know anymore because they changed. </p>
  
  <p>I know the group get removed after every member has been unregistered but i don't know the registration ids to unregister them manually. </p>
  
  <p>What can I do?</p>
  
  <p>Is there a way to retrieve the members of a device group or deleting it at once?</p>
  
  <p>Also, what is a good way to manage the case in which the token gets refreshed ?</p>