Upgrade the ReduxExample app (use CRNA) (#2171)

* [ReduxExample] Delete android and ios dirs

* [ReduxExample] Upgrade using create-react-native-app

* [ReduxExample] Add postinstall script to clean up files Yarn copies in

Yarn copies them when installing locally, causing lots of @proviesModule collisions.

* [ReduxExample] Upgrade expo and other dependencies

* [ReduxExample] Don't delete .git just in case

examples/ReduxExample/App.test.js

@@ -0,0 +1,9 @@
+import React from 'react';
+import App from './App';
+
+import renderer from 'react-test-renderer';
+
+it('renders without crashing', () => {
+  const rendered = renderer.create(<App />).toJSON();
+  expect(rendered).toBeTruthy();
+});