docs(sidenav): get rid of custom JS for active state

site/assets/js/application.js

@@ -19,19 +19,6 @@
     return [].slice.call(list)
   }
 
-  makeArray(document.querySelectorAll('.js-sidenav-group'))
-    .forEach(function (sidenavGroup) {
-      var groupHasLinks = Boolean(sidenavGroup.querySelector('li'))
-      var groupLink = sidenavGroup.querySelector('a')
-
-      if (groupHasLinks) {
-        groupLink.addEventListener('click', function (e) {
-          e.preventDefault()
-          e.target.parentNode.classList.toggle('active')
-        }, true)
-      }
-    })
-
   // Tooltip and popover demos
   makeArray(document.querySelectorAll('.tooltip-demo'))
     .forEach(function (tooltip) {