finally stop polyfilling promises in 2021

bower.json

@@ -49,8 +49,7 @@
     "jszip": "Stuk/jszip#^3.1.5",
     "requirejs-plugins": "^1.0.3",
     "dragula.js": "3.7.2",
-    "MathJax": "3.0.5",
-    "es6-promise ": "4.2.4"
+    "MathJax": "3.0.5"
   },
   "resolutions": {
     "bootstrap": "^v4.0.0",

www/common/media-tag.js

@@ -794,9 +794,7 @@ var factory = function () {
     if (typeof(module) !== 'undefined' && module.exports) {
         module.exports = factory();
     } else if ((typeof(define) !== 'undefined' && define !== null) && (define.amd !== null)) {
-        define([
-            '/bower_components/es6-promise/es6-promise.min.js'
-        ], function () {
+        define([], function () {
             return factory();
         });
     } else {