public static void removeConnectListener(ConnectListener listener) {
    synchronized (existingSystemsLock) {
      synchronized (connectListeners) {
        connectListeners.remove(listener);
      }
    }
  }
Makes note of a <code>ConnectListener</code> whose <code>onConnect</code> method will be
invoked when a connection is created to a distributed system.

@return set of currently existing system connections
geode-core/src/main/java/org/apache/geode/distributed/internal/InternalDistributedSystem.java