Fix several issues with ES6 redeclaration checks

test/mjsunit/harmony/regress/regress-3426.js

Index: test/mjsunit/harmony/regress/regress-3426.js
diff --git a/test/mjsunit/regress/regress-debug-context-load.js b/test/mjsunit/harmony/regress/regress-3426.js
similarity index 61%
copy from test/mjsunit/regress/regress-debug-context-load.js
copy to test/mjsunit/harmony/regress/regress-3426.js
index 0b3c275f99b016825cd563a700772bbddb7e4bad..c3b11a1792f8c8adaf05788d9604a2c9c9f5dcde 100644
--- a/test/mjsunit/regress/regress-debug-context-load.js
+++ b/test/mjsunit/harmony/regress/regress-3426.js
@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --expose-debug-as debug
+// Flags: --harmony-scoping
 
-Debug = debug.Debug;
-Debug.setListener(null);
+assertThrows("(function() { 'use strict'; { let f; var f; } })", SyntaxError);