MDL-80676 core: Remove unnecessary aria-labelledby for action menu links

The aria-labelledby attribute for the action menu link's <a> tag is
unnecessary as the <span> tag containing the action menu link's text
is already within the <a> tag and already serves as the link's label by
default.

lib/templates/action_menu_link.mustache

@@ -27,12 +27,12 @@
     }
 }}
 {{^disabled}}
-    <a href="{{url}}" class="{{$actionmenulinkclasses}}aabtn {{classes}}{{/actionmenulinkclasses}}" {{#attributes}}{{name}}="{{value}}" {{/attributes}}{{#showtext}}aria-labelledby="actionmenuaction-{{instance}}"{{/showtext}}>
+    <a href="{{url}}" class="{{$actionmenulinkclasses}}aabtn {{classes}}{{/actionmenulinkclasses}}" {{#attributes}}{{name}}="{{value}}" {{/attributes}}>
         {{#icon}}
             {{#pix}}{{key}}, {{component}}, {{title}}{{/pix}}
         {{/icon}}
         {{#showtext}}
-            <span class="menu-action-text" id="actionmenuaction-{{instance}}">{{{text}}}</span>
+            <span class="menu-action-text">{{{text}}}</span>
         {{/showtext}}
     </a>
 {{/disabled}}