src: remove unnecessary call to SetHiddenPrototype in contextify

Currently the template for the global object is explicitly marked as
hidden. This is unnecessary since the global object is automatically
marked as hidden by V8. Getting rid of this call gets rid of the last
use of SetHiddenPrototype.

src/node_contextify.cc

@@ -140,7 +140,6 @@ class ContextifyContext {
     EscapableHandleScope scope(env->isolate());
     Local<FunctionTemplate> function_template =
         FunctionTemplate::New(env->isolate());
-    function_template->SetHiddenPrototype(true);
 
     function_template->SetClassName(sandbox_obj->GetConstructorName());