Revert of Use custom scrollbars for print preview on non-retina mac displays.

chrome/browser/resources/pdf/scrollbars_mac.css

-/* Copyright 2015 The Chromium Authors. All rights reserved.
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file. */
-
-/*
- * Imitate mac scrollbars on non-retina displays to workaround crbug.com/466039.
- */
-@media
-(-webkit-max-device-pixel-ratio: 1) {
-
-::-webkit-scrollbar {
-  height: 14px;
-  width: 14px;
-}
-
-::-webkit-scrollbar-track,
-::-webkit-scrollbar-corner {
-  background-color: rgb(242,242,242);
-}
-
-::-webkit-scrollbar-thumb:vertical,
-::-webkit-scrollbar-thumb:horizontal {
-  -webkit-border-radius: 7px;
-  background-color: rgb(198,198,198);
-  border: 3px solid rgb(242,242,242);
-}
-
-::-webkit-scrollbar-thumb:vertical:hover,
-::-webkit-scrollbar-thumb:horizontal:hover {
-  background-color: rgb(126,126,126);
-}
-
-}