message: build: delete umd.js from the final package
  This file is not necessary and breaks closure compiler.
diff: @@ -118,6 +118,15 @@ if (fs.existsSync(UMD_ROOT)) {
  addLicenseTextToFile(license, UMD_PKG + 'rxjs.umd.min.js');
  }
  +// remove umd.js/umd.d.ts files that are only needed for creation of the umd bundle
  +fs.removeSync(CJS_PKG + '/internal/umd.js');
  +fs.removeSync(CJS_PKG + '/internal/umd.js.map');
  +fs.removeSync(ESM5_PKG + '/internal/umd.js');
  +fs.removeSync(ESM5_PKG + '/internal/umd.js.map');
  +fs.removeSync(ESM2015_PKG + '/internal/umd.js');
  +fs.removeSync(ESM2015_PKG + '/internal/umd.js.map');
  +fs.removeSync(TYPE_PKG + '/internal/umd.d.ts');
  +
  function copySources(rootDir, packageDir, ignoreMissing) {
  // If we are ignoring missing directories, early return when source doesn't exist
  if (!fs.existsSync(rootDir)) {
  