test: cleanup parallel/test-fs-readfile-unlink.js

Changes var to const, != to !==, and assert.equal() to assert.strict
Equal()

PR-URL: #8764
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>

Author: nohman20

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

@@ -5,21 +5,20 @@ const fs = require('fs');
 const path = require('path');
 const dirName = path.resolve(common.fixturesDir, 'test-readfile-unlink');
 const fileName = path.resolve(dirName, 'test.bin');
-
-var buf = Buffer.alloc(512 * 1024, 42);
+const buf = Buffer.alloc(512 * 1024, 42);
 
 try {
   fs.mkdirSync(dirName);
 } catch (e) {
   // Ignore if the directory already exists.
-  if (e.code != 'EEXIST') throw e;
+  if (e.code !== 'EEXIST') throw e;
 }
 
 fs.writeFileSync(fileName, buf);
 
 fs.readFile(fileName, function(err, data) {
   assert.ifError(err);
-  assert.equal(data.length, buf.length);
+  assert.strictEqual(data.length, buf.length);
   assert.strictEqual(buf[0], 42);
 
   fs.unlinkSync(fileName);