code: function removeListener(event, eventHandler) {
      checkEventValid(event);
  
      if (listeners[event] && listeners[event].length) {
          var indexOfListener = listeners[event].indexOf(eventHandler);
          if (indexOfListener > -1) {
              listeners[event].splice(indexOfListener, 1);
          }
      }
  }
docs: Remove a certain event listener
  @param {events} event - The name of the event to listen to
  @param {function} eventHandler - The eventHandler that is bound to this listener and should be removed