code: function listenOnce (element, eventType, listener, optEvtListenerOpts) {
    let unlisten = listen(element, eventType, event => {
      unlisten()
      listener(event)
    }, optEvtListenerOpts)
    return unlisten
  }
docs: Listens for the specified event on the element and removes the listener
  as soon as event has been received.
  @param {!EventTarget} element
  @param {string} eventType
  @param {function(!Event)} listener
  @param {Object=} optEvtListenerOpts
  @return {!UnlistenDef}