Don't force display the addUser button. Also, remove cancelAdduser.

BUG=412754

Review URL: https://codereview.chromium.org/562303002

Cr-Commit-Position: refs/heads/master@{#294518}

chrome/browser/resources/user_manager/control_bar.html

@@ -4,7 +4,6 @@
   </div>
   <div id="add-user-header-bar-item" class="header-bar-item">
     <button id="add-user-button" i18n-content="addUser"></button>
-    <button id="cancel-add-user-button" i18n-content="cancel" hidden></button>
   </div>
   <div class="header-bar-item">
     <div id="logo"></div>

chrome/browser/resources/user_manager/control_bar.js

@@ -30,8 +30,6 @@ cr.define('login', function() {
     decorate: function() {
       $('add-user-button').addEventListener('click',
           this.handleAddUserClick_);
-      $('cancel-add-user-button').addEventListener('click',
-          this.handleCancelAddUserClick_);
       $('guest-user-header-bar-item').addEventListener('click',
           this.handleGuestClick_);
       $('guest-user-button').addEventListener('click',
@@ -135,8 +133,6 @@ cr.define('login', function() {
      * @private
      */
     updateUI_: function() {
-      $('add-user-button').hidden = false;
-      $('cancel-add-user-button').hidden = !this.allowCancel_;
       $('guest-user-header-bar-item').hidden = false;
       $('add-user-header-bar-item').hidden = false;
     },