history-box: No need to unparent the stack

GTK cleans up for us

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Part-of: <https://gitlab.gnome.org/GNOME/calls/-/merge_requests/756>

src/calls-history-box.c

@@ -229,14 +229,11 @@ static void
 dispose (GObject *object)
 {
   CallsHistoryBox *self = CALLS_HISTORY_BOX (object);
-  GtkWidget *stack = GTK_WIDGET (self->stack);
 
   g_clear_signal_handler (&self->model_changed_handler_id, self->model);
   g_clear_object (&self->slice_model);
   g_clear_object (&self->model);
 
-  g_clear_pointer (&stack, gtk_widget_unparent);
-
   G_OBJECT_CLASS (calls_history_box_parent_class)->dispose (object);
 }