[gnome-contacts/wip/nielsdg/headergroup-warning] window: Remove unused header_group field

[Niels De Graef <nielsdg src gnome org>]

commit 1f1500ca01098ffda6392f5ec9ce3a29a48a84b1
Author: Niels De Graef <nielsdegraef gmail com>
Date:   Sat Jun 1 17:00:41 2019 +0200

    window: Remove unused header_group field
    
    This was giving an annoying warning.

 src/contacts-window.vala | 3 ---
 1 file changed, 3 deletions(-)
---
diff --git a/src/contacts-window.vala b/src/contacts-window.vala
index 49f6995..bcd632f 100644
--- a/src/contacts-window.vala
+++ b/src/contacts-window.vala
@@ -59,9 +59,6 @@ public class Contacts.Window : Gtk.ApplicationWindow {
   private Button cancel_button;
   [GtkChild]
   private Button done_button;
-  // Somehow needed for the header group to work
-  [GtkChild]
-  private HeaderGroup header_group;
 
   // The 2 panes the window consists of
   private ListPane list_pane;