code: function removeListener(priv, eventName, listener) {
    check(eventName, 'eventName').is.aString.and.oneOf(EVENT_NAMES)();
    var listeners = getListeners(priv, eventName);
    check(listener, 'listener').is.aFunction.and.is.oneOf(listeners, 'registered listeners')();
  
    listeners.splice(listeners.indexOf(listener), 1);
  }
docs: Unregisters a listener from given eventName.
  
  @param {String} eventName name of event
  @param {Function} listener a function
  @precondition given listener was previously passed to ${link Slider.prototype.on}
  @postcondition given listener will no longer be notified about current slide changes
  @fqn Slider.prototype.removeListener