Removed aria label from header and add it to nav

lms/templates/navigation.html

@@ -36,8 +36,8 @@ site_status_msg = get_site_status_msg(course_id)
 % endif
 </%block>
 
-  <header id="global-navigation" class="global ${"slim" if course else ""}" aria-label="${_('Global Navigation')}">
-    <nav aria-labelledby="global-navigation">
+  <header id="global-navigation" class="global ${"slim" if course else ""}" >
+    <nav aria-label="${_('Global')}">
     <h1 class="logo">
       <a href="${marketing_link('ROOT')}">
         <%block name="navigation_logo">