test: use common.fixtures.path()

PR-URL: https://github.com/nodejs/node/pull/16112
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>

test/parallel/test-fs-readfile-fd.js

@@ -1,9 +1,9 @@
 'use strict';
-const common = require('../common');
+require('../common');
+const fixtures = require('../common/fixtures');
 const assert = require('assert');
-const path = require('path');
 const fs = require('fs');
-const fn = path.join(common.fixturesDir, 'empty.txt');
+const fn = fixtures.path('empty.txt');
 
 tempFd(function(fd, close) {
   fs.readFile(fd, function(err, data) {