code: public ResponseWrapper retractMessage(String username, long msgId)
              throws APIConnectionException, APIRequestException {
          return _messageClient.retractMessage(username, msgId);
      }
docs: retract message
  消息撤回
  @param username 用户名
  @param msgId message id
  @return No Content， Error Code：
  855001 out of retract message time, the effective time is within 3 minutes after sending message
  855003 the retract message is not exist
  855004 the message had been retracted
  @throws APIConnectionException connect exception
  @throws APIRequestException request exception