message: remove some remaining dead code
diff: /*
  Copyright 2018 New Vector Ltd
  +Copyright 2020 The Matrix.org Foundation C.I.C.
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  @@ -16,40 +17,6 @@ limitations under the License.
  import React from "react";
  -// derived from code from github.com/noeldelgado/gemini-scrollbar
  -// Copyright (c) Noel Delgado <pixelia.me@gmail.com> (pixelia.me)
  -function getScrollbarWidth() {
  - const div = document.createElement('div');
  - div.className = 'mx_AutoHideScrollbar'; //to get width of css scrollbar
  - div.style.position = 'absolute';
  - div.style.top = '-9999px';
  - div.style.width = '100px';
  - div.style.height = '100px';
  - div.style.overflow = "scroll";
  - div.style.msOverflowStyle = '-ms-autohiding-scrollbar';
  - document.body.appendChild(div);
  - const scrollbarWidth = (div.offsetWidth - div.clientWidth);
  - document.body.removeChild(div);
  - return scrollbarWidth;
  -}
  -
  -function install() {
  - const scrollbarWidth = getScrollbarWidth();
  - if (scrollbarWidth !== 0) {
  - document.body.classList.add("mx_scrollbar_noautohide");
  - }
  -}
  -
  -const installBodyClassesIfNeeded = (function() {
  - let installed = false;
  - return function() {
  - if (!installed) {
  - install();
  - installed = true;
  - }
  - };
  -})();
  -
  export default class AutoHideScrollbar extends React.Component {
  constructor(props) {
  super(props);
  