test: use common/fixtures in tls-connect-no-host

PR-URL: nodejs/node#15986
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-tls-connect-no-host.js

@@ -1,17 +1,16 @@
 'use strict';
 const common = require('../common');
+const fixtures = require('../common/fixtures');
 
 if (!common.hasCrypto)
   common.skip('missing crypto');
 
 const tls = require('tls');
 
 const assert = require('assert');
-const fs = require('fs');
-const path = require('path');
 
-const cert = fs.readFileSync(path.join(common.fixturesDir, 'test_cert.pem'));
-const key = fs.readFileSync(path.join(common.fixturesDir, 'test_key.pem'));
+const cert = fixtures.readSync('test_cert.pem');
+const key = fixtures.readSync('test_key.pem');
 
 // https://github.com/nodejs/node/issues/1489
 // tls.connect(options) with no options.host should accept a cert with