code: public function off($eventType, $listener = null)
      {
          foreach ($this->_eventListeners as $i => $l) {
              if ($l->getType() == $eventType) {
                  if ($listener === null || $l->getListener() === $listener) {
                      unset($this->_eventListeners[$i]);
                  }
              }
          }
      }
docs: Removes an event listener.
  
  When $listener is null, this function removes all listeners linked to the event type.
  
  @param string   $eventType Event type
  @param Callable $listener  Listener (not required)
  
  @return void