[gtkmm] Gdk::Window: Remove add/remove_filter().

[Murray Cumming <murrayc src gnome org>]

commit f569a6c9f2cef8af19d629d0bbabf5d1c037212e
Author: Murray Cumming <murrayc murrayc com>
Date:   Sat Feb 10 10:58:18 2018 +0100

    Gdk::Window: Remove add/remove_filter().
    
    Because they were removed from GTK+ 4:
    https://gitlab.gnome.org/GNOME/gtk/commit/89f6b8751e79ba597fcbd8292df377fa98a7319f

 gdk/src/window.hg |    4 ----
 1 files changed, 0 insertions(+), 4 deletions(-)
---
diff --git a/gdk/src/window.hg b/gdk/src/window.hg
index 27ed706..52ac3b8 100644
--- a/gdk/src/window.hg
+++ b/gdk/src/window.hg
@@ -114,10 +114,6 @@ public:
   _WRAP_METHOD(void focus(guint32 timestamp), gdk_window_focus)
   _WRAP_METHOD(void set_user_data(gpointer user_data), gdk_window_set_user_data)
 
-  //We could wrap these with a Slot instead of a C callback, but these methods are very low-level anyway.
-  _WRAP_METHOD(void add_filter(GdkFilterFunc function, gpointer data), gdk_window_add_filter)
-  _WRAP_METHOD(void remove_filter(GdkFilterFunc function, gpointer data), gdk_window_remove_filter)
-
   _WRAP_METHOD(void scroll(int dx, int dy), gdk_window_scroll)
   _WRAP_METHOD(void move_region(const ::Cairo::RefPtr< ::Cairo::Region>& region, int dx, int dy), 
gdk_window_move_region)