[gtkmm] Gtk::Clipboard: Remove an obsolete comment

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 3421e2f441b66a48af673ac79173763364ebc2cb
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Jul 20 19:04:32 2017 +0200

    Gtk::Clipboard: Remove an obsolete comment
    
    gtk_clipboard_get_default() is now defined in gtkclipboard-quartz.c.

 gtk/src/clipboard.hg |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)
---
diff --git a/gtk/src/clipboard.hg b/gtk/src/clipboard.hg
index b0af1b4..d7f94a3 100644
--- a/gtk/src/clipboard.hg
+++ b/gtk/src/clipboard.hg
@@ -67,8 +67,6 @@ class Clipboard : public Glib::Object
 public:
   // It's unnecessary to wrap gtk_clipboard_get_default(). The wrapper would be
   // identical to get_for_display() with the default value of GdkAtom selection.
-  // If you ever wrap it, first make sure it's defined in gtkclipboard-quartz.c.
-  // https://bugzilla.gnome.org/show_bug.cgi?id=772281#c12
   _IGNORE(gtk_clipboard_get_default)
 
   _WRAP_METHOD(static Glib::RefPtr<Clipboard> get(GdkAtom selection = GDK_SELECTION_CLIPBOARD), 
gtk_clipboard_get, refreturn)