Remove unused App.test.js file

ui/src/App.test.js

@@ -1,9 +0,0 @@
-import React from 'react'
-import ReactDOM from 'react-dom'
-import App from './App'
-
-it('renders without crashing', () => {
-  const div = document.createElement('div')
-  ReactDOM.render(<App />, div)
-  ReactDOM.unmountComponentAtNode(div)
-})