test: normalize fixtures use

This commit replaces the use of `common.fixturesDir`
with `common.fixtures` & `fixtures.path` in
`test-fs-read-stream-resume.js`

PR-URL: #15855
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

test/parallel/test-fs-read-stream-resume.js

@@ -1,11 +1,11 @@
 'use strict';
-const common = require('../common');
+require('../common');
+const fixtures = require('../common/fixtures');
 const assert = require('assert');
 
 const fs = require('fs');
-const path = require('path');
 
-const file = path.join(common.fixturesDir, 'x.txt');
+const file = fixtures.path('x.txt');
 let data = '';
 let first = true;