[cleanup] delete dead code leftover from 48eff34

src/harmony-tostring.js

 // Copyright 2013 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.
 
 "use strict";
 
-// This file relies on the fact that the following declaration has been made
-// in runtime.js and symbol.js:
-// var $Object = global.Object;
-
-DefaultObjectToString = ObjectToStringHarmony;
-// ES6 draft 08-24-14, section 19.1.3.6
-function ObjectToStringHarmony() {
-  if (IS_UNDEFINED(this) && !IS_UNDETECTABLE(this)) return "[object Undefined]";
-  if (IS_NULL(this)) return "[object Null]";
-  var O = ToObject(this);
-  var builtinTag = %_ClassOf(O);
-  var tag = O[symbolToStringTag];
-  if (!IS_STRING(tag)) {
-    tag = builtinTag;
-  }
-  return "[object " + tag + "]";
-}
-
 function HarmonyToStringExtendSymbolPrototype() {
   %CheckIsBootstrapping();
 
   InstallConstants(global.Symbol, $Array(
     // TODO(dslomov, caitp): Move to symbol.js when shipping
    "toStringTag", symbolToStringTag
   ));
 }
 
 HarmonyToStringExtendSymbolPrototype();