[uber page] Remove obsolete subpage logic.

chrome/browser/resources/options2/options_page.css

 /* Copyright (c) 2012 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 {
   position: relative;
 }
 
 #main-content {
   bottom: 0;
   display: -webkit-box;
   left: 0;
   position: absolute;
   right: 0;
   top: 0;
 }
 
 #mainview {
   -webkit-box-align: stretch;
   bottom: 0;
   left: 0;
   margin: 0;
   position: absolute;
   right: 0;
   top: 0;
   z-index: 1;
 }
 
-html.hide-menu #mainview {
-  -webkit-padding-start: 0;
-}
-
 #mainview-content {
   min-height: 100%;
   position: relative;
 }
 
 #page-container {
   -webkit-padding-end: 24px;
   box-sizing: border-box;
   max-width: 888px;
   min-width: 600px;
@@ skipping 563 matching lines @@
       url('chrome://theme/IDR_CONTROLLED_SETTING_RECOMMENDED_LARGE');
 }
 
 html[dir='rtl'] .controlled-setting-bubble-text {
   background-position: right top;
 }
 
 .controlled-setting-bubble-action {
   padding: 0 !important;
 }