cleanup: drop polyfills which were required for IE11

package-lock.json

         "babel-types": "^6.24.1"
       }
     },
-    "babel-polyfill": {
-      "version": "6.26.0",
-      "resolved": "https://registry.npmjs.org/babel-polyfill/-/babel-polyfill-6.26.0.tgz",
-      "integrity": "sha1-N5k3q8Z9eJWXCtxiHyhM2WbPIVM=",
-      "dev": true,
-      "requires": {
-        "babel-runtime": "^6.26.0",
-        "core-js": "^2.5.0",
-        "regenerator-runtime": "^0.10.5"
-      },
-      "dependencies": {
-        "regenerator-runtime": {
-          "version": "0.10.5",
-          "resolved": "https://registry.npmjs.org/regenerator-runtime/-/regenerator-runtime-0.10.5.tgz",
-          "integrity": "sha1-M2w+/BIgrc7dosn6tntaeVWjNlg=",
-          "dev": true
-        }
-      }
-    },
     "babel-preset-env": {
       "version": "1.6.1",
       "resolved": "https://registry.npmjs.org/babel-preset-env/-/babel-preset-env-1.6.1.tgz",

package.json

     "babel-core": "6.26.0",
     "babel-eslint": "8.0.3",
     "babel-loader": "7.1.2",
-    "babel-polyfill": "6.26.0",
     "babel-preset-env": "1.6.1",
     "babel-preset-react": "6.24.1",
     "babel-preset-stage-1": "6.24.1",
     "string-replace-loader": "1.3.0",
     "style-loader": "0.19.0",
     "uglifyjs-webpack-plugin": "1.2.2",
-    "whatwg-fetch": "2.0.3",
     "webpack": "3.9.1",
     "webpack-dev-server": "2.9.5"
   },

react/features/base/lib-jitsi-meet/_.web.js

-/* @flow */
-
-// Polyfill URL for Internet Explorer.
-import 'url-polyfill';
+// @flow
 
 declare var JitsiMeetJS: Object;
 

webpack.config.js

 
             loader: 'expose-loader?$!expose-loader?jQuery',
             test: /\/node_modules\/jquery\/.*\.js$/
-        }, {
-            // Set scope to window for URL polyfill.
-
-            loader: 'imports-loader?this=>window',
-            test: /\/node_modules\/url-polyfill\/.*\.js$/
         }, {
             // Allow CSS to be imported into JavaScript.
 
 module.exports = [
     Object.assign({}, config, {
         entry: {
-            'app.bundle': [
-
-                // babel-polyfill and fetch polyfill are required for IE11.
-                'babel-polyfill',
-                'whatwg-fetch',
-                './app.js'
-            ],
+            'app.bundle': './app.js',
 
             'device_selection_popup_bundle':
                 './react/features/settings/popup.js',
 
             'dial_in_info_bundle': [
 
-                // babel-polyfill and fetch polyfill are required for IE11.
-                'babel-polyfill',
-                'whatwg-fetch',
-
                 // atlaskit does not support React 16 prop-types
                 './react/features/base/react/prop-types-polyfill.js',
 
     // JitsiMeetExternalAPI).
     Object.assign({}, config, {
         entry: {
-            'external_api': [
-
-                // XXX Required by at least IE11 at the time of this writing.
-                'babel-polyfill',
-                './modules/API/external/index.js'
-            ]
+            'external_api': './modules/API/external/index.js'
         },
         output: Object.assign({}, config.output, {
             library: 'JitsiMeetExternalAPI',