[intrinsic] Drop the %_ValueOf intrinsic.

src/js/string.js

Index: src/js/string.js
diff --git a/src/js/string.js b/src/js/string.js
index b3bc3933cda29b04a3253f74d6949c85419f7231..5180e3056fa55c374531eaf0545a99b109f0f321 100644
--- a/src/js/string.js
+++ b/src/js/string.js
@@ -37,24 +37,6 @@ utils.Import(function(from) {
 
 //-------------------------------------------------------------------
 
-// ECMA-262 section 15.5.4.2
-function StringToString() {
-  if (!IS_STRING(this) && !IS_STRING_WRAPPER(this)) {
-    throw MakeTypeError(kNotGeneric, 'String.prototype.toString');
-  }
-  return %_ValueOf(this);
-}
-
-
-// ECMA-262 section 15.5.4.3
-function StringValueOf() {
-  if (!IS_STRING(this) && !IS_STRING_WRAPPER(this)) {
-    throw MakeTypeError(kNotGeneric, 'String.prototype.valueOf');
-  }
-  return %_ValueOf(this);
-}
-
-
 // ECMA-262, section 15.5.4.6
 function StringConcat(other /* and more */) {  // length == 1
   "use strict";
@@ -756,8 +738,6 @@ utils.InstallFunctions(GlobalString, DONT_ENUM, [
 
 // Set up the non-enumerable functions on the String prototype object.
 utils.InstallFunctions(GlobalString.prototype, DONT_ENUM, [
-  "valueOf", StringValueOf,
-  "toString", StringToString,
   "codePointAt", StringCodePointAt,
   "concat", StringConcat,
   "endsWith", StringEndsWith,