Remove old isHidden function

src/librustdoc/html/static/main.js

@@ -3,7 +3,7 @@
 
 // Local js definitions:
 /* global addClass, getCurrentValue, hasClass */
-/* global isHidden, onEach, removeClass, updateLocalStorage */
+/* global onEach, removeClass, updateLocalStorage */
 
 if (!String.prototype.startsWith) {
     String.prototype.startsWith = function(searchString, position) {

src/librustdoc/html/static/storage.js

@@ -24,10 +24,6 @@ function removeClass(elem, className) {
     elem.classList.remove(className);
 }
 
-function isHidden(elem) {
-    return elem.offsetParent === null;
-}
-
 function onEach(arr, func, reversed) {
     if (arr && arr.length > 0 && func) {
         var length = arr.length;