Docs: remove note about TypeScript files requiring at least one export (#7260)

Author: MidnightDesign

docusaurus/docs/running-tests.md

@@ -111,8 +111,6 @@ import Adapter from 'enzyme-adapter-react-16';
 configure({ adapter: new Adapter() });
 ```
 
-> Note: When using TypeScript with Babel, all your files need to have at least one export, otherwise you will get the error `Cannot compile namespaces when the '--isolatedModules' flag is provided.`. To fix this, you can add `export default undefined` to `src/setupTests.ts`.
-
 > Note: Keep in mind that if you decide to "eject" before creating `src/setupTests.js`, the resulting `package.json` file won't contain any reference to it. [Read here](#initializing-test-environment) to learn how to add this after ejecting.
 
 Now you can write a smoke test with it: