Remove extra debug line from Object.prototype.toString

Fixes mozilla failures
Review URL: http://codereview.chromium.org/6935020

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7787 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/v8natives.js

@@ -1199,7 +1199,6 @@ function FunctionSourceString(func) {
   }
 
   var source = %FunctionGetSourceCode(func);
-  if (!IS_STRING(source)) return "NOT A string";
   if (!IS_STRING(source) || %FunctionIsBuiltin(func)) {
     var name = %FunctionGetName(func);
     if (name) {