[Hotword] Remove unneeded preferences. Cleaning up look of settings.

chrome/browser/resources/options/browser_options.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. */
 
 #change-home-page-section {
   margin-left: 30px;
 }
 
 #home-page-url {
   display: inline-block;
@@ skipping 142 matching lines @@
  * of pages that depend on it.
  * TODO(kevers): Rivisit padding rules. */
 #default-search-engine {
   padding-bottom: 0;
 }
 
 .hotword-settings {
   -webkit-margin-start: 22px;
 }
 
-#hotword-search-description {
-  color: #9b9b9b;
-}
-
 /* Internet settings */
 
 #network-settings {
   position: relative;
 }
 
 #network-list {
   min-height: 0;
   width: 320px;
 }
@@ skipping 249 matching lines @@
 }
 
 #accessibility-autoclick .controlled-setting-with-label {
   -webkit-box-align: baseline;
 }
 
 #accessibility-autoclick label + select {
   /* Same as .controlled-setting-with-label > input + span. */
   -webkit-margin-start: 0.6em;
 }