[gtk+] Remove an unused variable

[Matthias Clasen <matthiasc src gnome org>]

commit 577e9a33bb5e3a7409dd8a0b131e8224cbbb3844
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Jun 13 17:49:06 2015 -0400

    Remove an unused variable

 gdk/gdkwindow.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)
---
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 8edaa55..612d796 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -198,8 +198,6 @@ static guint signals[LAST_SIGNAL] = { 0 };
 
 static gpointer parent_class = NULL;
 
-static const cairo_user_data_key_t gdk_window_cairo_key;
-
 G_DEFINE_ABSTRACT_TYPE (GdkWindow, gdk_window, G_TYPE_OBJECT)
 
 #ifdef DEBUG_WINDOW_PRINTING