[es6] don't "replace" Object.prototype.toString for --harmony-tostring

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;
 
@@ skipping 14 matching lines @@
 function HarmonyToStringExtendSymbolPrototype() {
   %CheckIsBootstrapping();
 
   InstallConstants(global.Symbol, $Array(
     // TODO(dslomov, caitp): Move to symbol.js when shipping
    "toStringTag", symbolToStringTag
   ));
 }
 
 HarmonyToStringExtendSymbolPrototype();
-
-function HarmonyToStringExtendObjectPrototype() {
-  %CheckIsBootstrapping();
-
-  // Can't use InstallFunctions() because will fail in Debug mode.
-  // Emulate InstallFunctions() here.
-  %FunctionSetName(ObjectToStringHarmony, "toString");
-  %FunctionRemovePrototype(ObjectToStringHarmony);
-  %SetNativeFlag(ObjectToStringHarmony);
-
-  // Set up the non-enumerable functions on the Array prototype object.
-  var desc = ToPropertyDescriptor({
-    value: ObjectToStringHarmony
-  });
-  DefineOwnProperty($Object.prototype, "toString", desc, false);
-
-  %ToFastProperties($Object.prototype);
-}
-
-HarmonyToStringExtendObjectPrototype();