Remove core-js/regenerator-runtime stubs (#6755)

packages/babel-polyfill/scripts/make-separate-polyfill-files.js

@@ -1,25 +0,0 @@
-"use strict";
-
-const fs = require("fs");
-const path = require("path");
-
-function relative(loc) {
-  return path.join(__dirname, "..", loc);
-}
-
-const builtIns = require("@babel/preset-env/data/built-ins.json");
-const polyfills = Object.keys(builtIns);
-
-polyfills
-  .concat(["web.timers", "web.immediate", "web.dom.iterable"])
-  .forEach(polyfill => {
-    fs.writeFileSync(
-      relative(`src/core-js/modules/${polyfill}.js`),
-      `require("core-js/modules/${polyfill}");`
-    );
-  });
-
-fs.writeFileSync(
-  relative("src/regenerator-runtime/runtime.js"),
-  'require("regenerator-runtime/runtime");'
-);