Fix keyboard navigation in course outline

Remove some obsolete and broken a11y markup that was causing
keyboard navigation in the main course outline to focus elements
that shouldn't be focused.

LEARNER-2893

openedx/features/course_experience/templates/course_experience/course-outline-fragment.html

@@ -14,25 +14,19 @@ from openedx.core.djangolib.markup import HTML, Text
 
 <main role="main" class="course-outline" id="main" tabindex="-1">
     % if blocks.get('children'):
-        <ol class="block-tree" role="tree">
+        <ol class="block-tree">
             % for section in blocks.get('children'):
                 <li
-                    aria-expanded="true"
                     class="outline-item focusable section"
                     id="${ section['id'] }"
-                    role="treeitem"
-                    tabindex="0"
                 >
                     <div class="section-name">
                         <h3 class="section-title">${ section['display_name'] }</h3>
                     </div>
-                    <ol class="outline-item focusable" role="group" tabindex="0">
+                    <ol class="outline-item focusable">
                         % for subsection in section.get('children', []):
                             <li
                                 class="subsection ${ 'current' if subsection['last_accessed'] else '' }"
-                                role="treeitem"
-                                tabindex="-1"
-                                aria-expanded="true"
                             >
                                 <a
                                     class="outline-item focusable"
@@ -107,7 +101,6 @@ from openedx.core.djangolib.markup import HTML, Text
                                     <div class="subsection-actions">
                                         ## Resume button (if last visited section)
                                         % if subsection['last_accessed']:
-                                            <span class="sr-only">${ _("This is your last visited course section.") }</span>
                                             <span class="resume-right">
                                                 <b>${ _("Resume Course") }</b>
                                                 <span class="icon fa fa-arrow-circle-right" aria-hidden="true"></span>