code: func (m *Manager) DeleteRegistryEntry(username string, globalid string, key string) (err error) {
  	selector, err := createSelector(username, globalid, key)
  	if err != nil {
  		return
  	}
  
  	_, err = m.getRegistryCollection().UpdateAll(
  		selector,
  		bson.M{"$pull": bson.M{"entries": bson.M{"key": key}}})
  
  	return
  }
docs: //DeleteRegistryEntry deletes a registry entry
  // Either a username or a globalid needs to be given
  // If the key does not exist, no error is returned