gsourceclosure: use g_cclosure_marshal_generic

For the glib-defined source types, and any source type that defines a
closure callback but not a closure marshal, use
g_cclosure_marshal_generic. And then remove all the other remaining
source closure marshals.

https://bugzilla.gnome.org/show_bug.cgi?id=701511

gio/gasynchelper.c

@@ -109,37 +109,12 @@ fd_source_closure_callback (int           fd,
   return result;
 }
 
-static void
-fd_source_closure_marshal (GClosure     *closure,
-			   GValue       *return_value,
-			   guint         n_param_values,
-			   const GValue *param_values,
-			   gpointer      invocation_hint,
-			   gpointer      marshal_data)
-{
-  GFDSourceFunc callback;
-  GCClosure *cc = (GCClosure*) closure;
-  gboolean v_return;
-
-  g_return_if_fail (return_value != NULL);
-  g_return_if_fail (n_param_values == 0);
-
-  callback = (GFDSourceFunc) (marshal_data ? marshal_data : cc->callback);
-
-  v_return = callback (g_value_get_int (param_values),
-                       g_value_get_flags (param_values + 1),
-		       closure->data);
-
-  g_value_set_boolean (return_value, v_return);
-}
-
 static GSourceFuncs fd_source_funcs = {
   fd_source_prepare,
   fd_source_check,
   fd_source_dispatch,
   fd_source_finalize,
   (GSourceFunc)fd_source_closure_callback,
-  (GSourceDummyMarshal)fd_source_closure_marshal,
 };
 
 GSource *