MD Settings: Remove leftover aria-describedby in Supervised Users link

chrome/browser/resources/settings/people_page/people_page.html

 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_expand_button/cr_expand_button.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/icon.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/util.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-collapse/iron-collapse.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable.html">
@@ skipping 267 matching lines @@
               is="paper-icon-button-light" aria-label="$i18n{importTitle}">
           </button>
         </div>
 </if>
 
         <template is="dom-if" if="[[profileManagesSupervisedUsers_]]">
           <div id="manageSupervisedUsersContainer" class="settings-box"
               on-tap="onManageSupervisedUsers_" actionable>
             <div class="start">$i18n{manageSupervisedUsers}</div>
             <button class="icon-external" is="paper-icon-button-light"
-                aria-label="$i18n{manageSupervisedUsers}"
-                aria-describedby="manageSupervisedUsersSecondary"></button>
+                aria-label="$i18n{manageSupervisedUsers}"></button>
           </div>
         </template>
       </neon-animatable>
       <template is="dom-if" route-path="/syncSetup"
           no-search$="[[!isAdvancedSyncSettingsVisible_(syncStatus)]]">
         <settings-subpage
             associated-control="[[$$('#sync-status')]]"
             page-title="$i18n{syncPageTitle}"
             no-search$="[[!isAdvancedSyncSettingsVisible_(syncStatus)]]">
           <settings-sync-page></settings-sync-page>
@@ skipping 98 matching lines @@
 <if expr="chromeos">
     <template is="dom-if" if="[[showEasyUnlockTurnOffDialog_]]">
       <easy-unlock-turn-off-dialog id="easyUnlockTurnOffDialog"
           on-close="onEasyUnlockTurnOffDialogClose_">
       </easy-unlock-turn-off-dialog>
     </template>
 </if>
   </template>
   <script src="people_page.js"></script>
 </dom-module>