test: used fixturesDir from fixtures modules

In test-fs-realpath-on-substed-drive:

Require common/fixtures module and swapped the location of fixturesDir
from common to fixtures module.

test/parallel/test-fs-realpath-on-substed-drive.js

@@ -4,6 +4,8 @@ const common = require('../common');
 if (!common.isWindows)
   common.skip('Test for Windows only');
 
+const fixtures = require('../common/fixtures');
+
 const assert = require('assert');
 const fs = require('fs');
 const spawnSync = require('child_process').spawnSync;
@@ -16,7 +18,7 @@ let drive;
 let i;
 for (i = 0; i < driveLetters.length; ++i) {
   drive = `${driveLetters[i]}:`;
-  result = spawnSync('subst', [drive, common.fixturesDir]);
+  result = spawnSync('subst', [drive, fixtures.fixturesDir]);
   if (result.status === 0)
     break;
 }