Remove some unused resources.

chrome/browser/resources/local_discovery/local_discovery.css

 /* Copyright 2013 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. */
 
 body {
   margin: 21px 10px 24px 10px;
 }
 
 h1 {
   margin: 0 0 13px 0;
@@ skipping 97 matching lines @@
 
 section {
   margin-bottom: 23px;
 }
 
 .dialog-contents {
     padding-left: 17px;
 }
 
 #back-link {
-  background: url(chrome://theme/IDR_CHEVRON_LEFT) left no-repeat;
+  background: -webkit-image-set(
+      url(chevron_left-1x.png) 1x,
+      url(chevron_left-2x.png) 2x)
+      no-repeat;
   margin-bottom: 25px;
   margin-top: 6px;
   padding-left: 23px;
 }
 
 html[dir='rtl'] #back-link {
   transform: scaleX(-1);
 }
 
 html[dir='rtl'] #back-link span {
   display: inline-block;
   transform: scaleX(-1);
 }