Removed the tab wrapper tabindex

Closes #3381033

js/quicktabs.js

@@ -44,7 +44,6 @@ Drupal.quicktabs.clickHandler = function(event) {
   // https://www.w3.org/TR/wai-aria-practices-1.1/examples/tabs/tabs-2/tabs.html
   $(this).parents('li').siblings().removeClass('active');
   $(this).parents('li').siblings().attr('aria-selected', 'false');
-  $(this).parents('li').siblings().attr('tabindex', '-1');
   $(this).parents('li').siblings().find('a').attr('tabindex', '-1');
   $(this).parents('li').addClass('active');
   $(this).parents('li').attr('aria-selected', 'true');