Cleanup: Move mjsunit/regress-*.js into mjsunit/regress/.

test/mjsunit/regress-4399.js

Index: test/mjsunit/regress-4399.js
diff --git a/test/mjsunit/regress-4399.js b/test/mjsunit/regress-4399.js
deleted file mode 100644
index a8fdab7d9d62dfa33d34987f8994536e5dc762cc..0000000000000000000000000000000000000000
--- a/test/mjsunit/regress-4399.js
+++ /dev/null
@@ -1,8 +0,0 @@
-// Copyright 2015 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-
-if (this.Worker) {
-  assertThrows(function() { Worker.prototype.constructor("55"); });
-}