Remove use of pify from the static-server script (#18239)

The static server script no longer uses `pify`. `pify` was being used
to promisify the `fs.stat` function, but that function has a built-in
Promise-supporting API that is now used instead.

development/static-server.js

@@ -1,14 +1,13 @@
 #!/usr/bin/env node
-const fs = require('fs');
+const fs = require('fs').promises;
 const path = require('path');
 
 const chalk = require('chalk');
-const pify = require('pify');
 
 const createStaticServer = require('./create-static-server');
 const { parsePort } = require('./lib/parse-port');
 
-const fsStat = pify(fs.stat);
+const fsStat = fs.stat;
 const DEFAULT_PORT = 9080;
 
 const onResponse = (request, response) => {