LMS: semantically hides the ie-centric browser warning/FF/Chrome suggestion…

LMS: semantically hides the ie-centric browser warning/FF/Chrome suggestion message to avoid confusing/misleading assistive tech-based users.

lms/templates/navigation.html

@@ -123,7 +123,7 @@ site_status_msg = get_site_status_msg(course_id)
   </nav>
 </header>
 % if course:
-<div class="ie-banner">${_('<strong>Warning:</strong> Your browser is not fully supported. We strongly recommend using {chrome_link_start}Chrome{chrome_link_end} or {ff_link_start}Firefox{ff_link_end}.').format(chrome_link_start='<a href="https://www.google.com/intl/en/chrome/browser/" target="_blank">', chrome_link_end='</a>', ff_link_start='<a href="http://www.mozilla.org/en-US/firefox/new/" target="_blank">', ff_link_end='</a>')}</div>
+<div class="ie-banner" aria-hidden="true">${_('<strong>Warning:</strong> Your browser is not fully supported. We strongly recommend using {chrome_link_start}Chrome{chrome_link_end} or {ff_link_start}Firefox{ff_link_end}.').format(chrome_link_start='<a href="https://www.google.com/intl/en/chrome/browser/" target="_blank">', chrome_link_end='</a>', ff_link_start='<a href="http://www.mozilla.org/en-US/firefox/new/" target="_blank">', ff_link_end='</a>')}</div>
 % endif
 
 %if not user.is_authenticated():