MD Extensions: Remove invalid </iron-list> closing tag.

Also remove dependency on iron-list since it is not actually used. This
reduces crisper.js output by 16% (from 173kb to 145kb)!

Bug: 764126
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Iab7e53b4e67e06f5ab54693e0c7b9df5ec0f677a
Reviewed-on: https://chromium-review.googlesource.com/747127Reviewed-by: Dave Schuyler <dschuyler@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512955}

chrome/browser/resources/md_extensions/error_page.html

@@ -8,7 +8,6 @@
 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-collapse/iron-collapse.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/iron-icons.html">
-<link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
@@ -206,7 +205,7 @@
                 </template>
               </div>
             </template>
-          </iron-list>
+          </div>
         </div>
       </div>
     </div>