Settings Router Refactor: Remove one last stray subpage-back.

chrome/browser/resources/settings/settings_page/settings_subpage.js

 // Copyright 2016 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.
 
 /**
  * @fileoverview
  * 'settings-subpage' shows a subpage beneath a subheader. The header contains
- * the subpage title and a back icon. The back icon fires an event which
- * is caught by settings-animated-pages, so it requires no separate handling.
+ * the subpage title and a back icon.
  */
 
 Polymer({
   is: 'settings-subpage',
 
   behaviors: [
     // TODO(michaelpg): phase out NeonAnimatableBehavior.
     Polymer.NeonAnimatableBehavior,
     Polymer.IronResizableBehavior,
   ],
@@ skipping 17 matching lines @@
      * @type {?HTMLElement}
      */
     associatedControl: {
       type: Object,
       value: null,
     },
   },
 
   /** @private */
   onTapBack_: function() {
-    // Event is caught by settings-animated-pages.
-    this.fire('subpage-back');
+    settings.navigateTo(assert(settings.getCurrentRoute().parent));
   },
 
   /** @private */
   onSearchChanged_: function(e) {
     this.searchTerm = e.detail;
   },
 });