code: function() {
            var self = this;
            $firebaseUtils.trimKeys(self, {});
            self.$value = null;
            return $firebaseUtils.doRemove(self.$ref()).then(function() {
              self.$$notify();
              return self.$ref();
            });
          }
docs: Removes all keys from the FirebaseObject and also removes
  the remote data from the server.
  
  @returns a promise which will resolve after the op completes