changesettracker: Delete IE8 compatibility code

Author: rhansen

src/static/js/changesettracker.js

@@ -136,15 +136,6 @@ const makeChangesetTracker = (scheduler, apool, aceCallbacksProvider) => {
         // that includes old submittedChangeset
         toSubmit = Changeset.compose(submittedChangeset, userChangeset, apool);
       } else {
-        // add forEach function to Array.prototype for IE8
-        if (!('forEach' in Array.prototype)) {
-          Array.prototype.forEach = function (action, that /* opt*/) {
-            for (let i = 0, n = this.length; i < n; i++) {
-              if (i in this) action.call(that, this[i], i, this);
-            }
-          };
-        }
-
         // Get my authorID
         const authorId = parent.parent.pad.myUserInfo.userId;