chore: remove unused deprecated polyfill.js file (#6345)

* config(dev): remove unused polyfills in webpack-dev

src/polyfills.js

@@ -1,12 +0,0 @@
-// Promise global, Used ( at least ) by 'whatwg-fetch'. And required by IE 11
-
-import win from "core/window"
-
-if(typeof win.Promise === "undefined") {
-  require("core-js/fn/promise")
-}
-
-// Required by IE 11
-if(!String.prototype.startsWith) {
-  require("core-js/es6/string")
-}

webpack/core.babel.js

@@ -14,7 +14,6 @@ const result = configBuilder(
   {
     entry: {
       "swagger-ui": [
-        // "./src/polyfills.js", // TODO: remove?
         "./src/index.js",
       ],
     },

webpack/dev.babel.js

@@ -18,11 +18,9 @@ const devConfig = configBuilder(
     mode: "development",
     entry: {
       "swagger-ui-bundle": [
-        "./src/polyfills.js", // TODO: remove?
         "./src/core/index.js",
       ],
       "swagger-ui-standalone-preset": [
-        "./src/polyfills", // TODO: remove?
         "./src/standalone/index.js",
       ],
       "swagger-ui": "./src/style/main.scss",