test: dont need to remove nonexistent directory

the TempDirection is empty , so tempdir/test1 and tempdir/test2
are nonexistent. we dont need to delete nonexistent directories.

PR-URL: #17119
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

test/parallel/test-fs-mkdir.js

@@ -15,8 +15,6 @@ common.refreshTmpDir();
 {
   const pathname = `${common.tmpDir}/test1`;
 
-  unlink(pathname);
-
   fs.mkdir(pathname, common.mustCall(function(err) {
     assert.strictEqual(err, null);
     assert.strictEqual(common.fileExists(pathname), true);
@@ -30,8 +28,6 @@ common.refreshTmpDir();
 {
   const pathname = `${common.tmpDir}/test2`;
 
-  unlink(pathname);
-
   fs.mkdir(pathname, 0o777, common.mustCall(function(err) {
     assert.strictEqual(err, null);
     assert.strictEqual(common.fileExists(pathname), true);