Merge pull request wmonk#305 from StevenLangbroek/fix_mjs_resolution

fix(modules): remove duplicate mjs from jest config

Author: wmonk

Diff for: packages/react-scripts/scripts/utils/createJestConfig.js

@@ -47,7 +47,6 @@ module.exports = (resolve, rootDir, isEjecting) => {
       '^react-native$': 'react-native-web',
     },
     moduleFileExtensions: [
-      'mjs',
       'web.ts',
       'ts',
       'web.tsx',