example: Convert _app.js to functional components (#10115)

Fix formatting

examples/with-app-layout/pages/_app.js

 import React from 'react'
-import App from 'next/app'
 
-class Layout extends React.Component {
-  render() {
-    const { children } = this.props
-    return <div className="layout">{children}</div>
-  }
-}
+const Layout = ({ children }) => <div className="layout">{children}</div>
 
-export default class MyApp extends App {
-  render() {
-    const { Component, pageProps } = this.props
-    return (
-      <Layout>
-        <Component {...pageProps} />
-      </Layout>
-    )
-  }
-}
+export default ({ Component, pageProps }) => (
+  <Layout>
+    <Component {...pageProps} />
+  </Layout>
+)