chore: remove-redundant-example-import (vercel#13175)

This issue is related to vercel#12964 

**I changed the following examples:**
`with-zeit-fetch` 
`with-why-did-you-render`
`with-styletron`
`custom-server-fastify`
`custom-server-express`
`with-why-did-you-render`
`custom-server-hapi`
`custom-server-koa`
`custom-server-polka`
`custom-server-typescript`
`progressive-render`
`ssr-caching`
`svg-components`
`using-preact`
`with-ant-design`

examples/custom-server-express/pages/index.js

@@ -1,4 +1,3 @@
-import React from 'react'
 import Link from 'next/link'
 
 export default function Home() {

examples/custom-server-fastify/pages/index.js

@@ -1,4 +1,3 @@
-import React from 'react'
 import Link from 'next/link'
 
 export default function Home() {

examples/custom-server-hapi/pages/a.js

@@ -1,5 +1,3 @@
-import React from 'react'
-
 export default function A() {
   return <div>a</div>
 }

examples/custom-server-hapi/pages/b.js

@@ -1,5 +1,3 @@
-import React from 'react'
-
 export default function B() {
   return <div>b</div>
 }

examples/custom-server-hapi/pages/index.js

@@ -1,4 +1,3 @@
-import React from 'react'
 import Link from 'next/link'
 
 export default function Home() {

examples/custom-server-koa/pages/index.js

@@ -1,4 +1,3 @@
-import React from 'react'
 import Link from 'next/link'
 
 export default function Home() {

examples/custom-server-polka/pages/a.js

@@ -1,5 +1,3 @@
-import React from 'react'
-
 export default function A() {
   return <div>a</div>
 }

examples/custom-server-polka/pages/b.js

@@ -1,5 +1,3 @@
-import React from 'react'
-
 export default function B() {
   return <div>b</div>
 }

examples/custom-server-polka/pages/index.js

@@ -1,4 +1,3 @@
-import React from 'react'
 import Link from 'next/link'
 
 export default function Home() {

examples/custom-server-typescript/pages/a.tsx

@@ -1,5 +1,3 @@
-import React from 'react'
-
 export default function A() {
   return <div>a</div>
 }

examples/custom-server-typescript/pages/b.tsx

@@ -1,5 +1,3 @@
-import React from 'react'
-
 export default function B() {
   return <div>b</div>
 }

examples/custom-server-typescript/pages/index.tsx

@@ -1,4 +1,3 @@
-import React from 'react'
 import Link from 'next/link'
 
 export default function Home() {

examples/ssr-caching/pages/blog/[id].js

@@ -1,5 +1,3 @@
-import React from 'react'
-
 export default function Post(props) {
   return (
     <div>

examples/svg-components/pages/index.js

@@ -1,4 +1,3 @@
-import React from 'react'
 import Cat from '../svgs/cat.svg'
 
 export default function Home() {

examples/using-preact/pages/index.js

@@ -1,4 +1,3 @@
-import React from 'react'
 import Link from 'next/link'
 
 export default function Home() {

examples/with-ant-design/pages/_app.js

@@ -1,4 +1,5 @@
 import React from 'react'
+
 import 'antd/dist/antd.css'
 import '../styles/vars.css'
 import '../styles/global.css'

examples/with-ant-design/pages/index.js

@@ -1,4 +1,3 @@
-import React from 'react'
 import { Form, Select, InputNumber, Switch, Slider, Button } from 'antd'
 
 // Custom DatePicker that uses Day.js instead of Moment.js

examples/with-zeit-fetch/pages/index.js

@@ -1,4 +1,3 @@
-import React from 'react'
 import Link from 'next/link'
 import fetch from '../fetch'