code: public static void unRegister(Class<? extends Event> eventClass, Subscriber subscriber) {
          CopyOnWriteArraySet<Subscriber> set = SUBSCRIBER_MAP.get(eventClass);
          if (set != null) {
              set.remove(subscriber);
              if (LOGGER.isDebugEnabled()) {
                  LOGGER.debug("UnRegister subscriber: {} of event: {}.", subscriber, eventClass);
              }
          }
      }
docs: 反注册一个订阅者
  
  @param eventClass 事件类型
  @param subscriber 订阅者