Replace admin devops callout clear button FA icon with GlIcon close

app/views/admin/dev_ops_report/_callout.html.haml

@@ -3,7 +3,7 @@
   .bordered-box.landing.content-block
     %button.btn.btn-default.close.js-close-callout{ type: 'button',
       'aria-label' => _('Dismiss DevOps Report introduction') }
-      = icon('times', class: 'dismiss-icon', 'aria-hidden' => 'true')
+      = sprite_icon('close', size: 16, css_class: 'dismiss-icon')
     .user-callout-copy
       %h4
         = _('Introducing Your DevOps Report')