refactor: Use native fs instead of fs-extra and promisify (vercel#13841)

**add-comment.js**
`writeFile` is not unique to `fs-extra`. 

**lib/find-page-file.ts**
ref: vercel#12026

.github/actions/next-stats-action/src/add-comment.js

@@ -1,5 +1,5 @@
 const path = require('path')
-const fs = require('fs-extra')
+const fs = require('fs').promises
 const fetch = require('node-fetch')
 const prettyMs = require('pretty-ms')
 const logger = require('./util/logger')

packages/next/server/lib/find-page-file.ts

@@ -2,18 +2,15 @@ import { join, sep as pathSeparator, normalize } from 'path'
 import chalk from 'next/dist/compiled/chalk'
 import { isWriteable } from '../../build/is-writeable'
 import { warn } from '../../build/output/log'
-import fs from 'fs'
-import { promisify } from 'util'
+import { promises } from 'fs'
 import { denormalizePagePath } from '../../next-server/server/normalize-page-path'
 
-const readdir = promisify(fs.readdir)
-
 async function isTrueCasePagePath(pagePath: string, pagesDir: string) {
   const pageSegments = normalize(pagePath).split(pathSeparator).filter(Boolean)
 
   const segmentExistsPromises = pageSegments.map(async (segment, i) => {
     const segmentParentDir = join(pagesDir, ...pageSegments.slice(0, i))
-    const parentDirEntries = await readdir(segmentParentDir)
+    const parentDirEntries = await promises.readdir(segmentParentDir)
     return parentDirEntries.includes(segment)
   })