public static void removeRegistrationListener(RegistrationListener l) {
    synchronized (listenersSync) {
      Set<RegistrationListener> newSet = new HashSet<>(listeners);
      newSet.remove(l);
      listeners = newSet;
    }
  }
Removes a {@code RegistrationListener} so that it no longer receives callbacks.
geode-core/src/main/java/org/apache/geode/internal/InternalDataSerializer.java