@Override
  public void removeJoinLeaveListener(JoinLeaveListener observer) {
    synchronized (listenersLock) {
      Set<JoinLeaveListener> oldListeners = listeners;
      if (oldListeners.contains(observer)) {
        Set<JoinLeaveListener> newListeners = new HashSet<>(oldListeners);
        if (newListeners.remove(observer)) {
          listeners = newListeners;
        }
      }
    }
  }
Deregisters a {@code JoinLeaveListener} from this agent.
geode-core/src/main/java/org/apache/geode/internal/admin/remote/RemoteGfManagerAgent.java