[geary] Remove compat definition of Binding.unbind and its one use.

[Michael Gratton <mjog src gnome org>]

commit 5d8519c70dec93c4a0c20c8d3b713137da6df7a9
Author: Michael James Gratton <mike vee net>
Date:   Sat Oct 8 17:44:03 2016 +1100

    Remove compat definition of Binding.unbind and its one use.

 src/client/components/main-toolbar.vala |    2 +-
 src/client/util/util-gtk.vala           |    6 ------
 2 files changed, 1 insertions(+), 7 deletions(-)
---
diff --git a/src/client/components/main-toolbar.vala b/src/client/components/main-toolbar.vala
index 5118f88..6f9441e 100644
--- a/src/client/components/main-toolbar.vala
+++ b/src/client/components/main-toolbar.vala
@@ -158,7 +158,7 @@ public class MainToolbar : Gtk.Box {
         remove(header);
         header.get_style_context().remove_class("geary-titlebar");
         header.get_style_context().remove_class("geary-titlebar-right");
-        GtkUtil.unbind(guest_header_binding);
+        guest_header_binding.unbind();
         header.show_close_button = false;
         header.decoration_layout = Gtk.Settings.get_default().gtk_decoration_layout;
         conversation_header.show();
diff --git a/src/client/util/util-gtk.vala b/src/client/util/util-gtk.vala
index 83eaa36..ae205e1 100644
--- a/src/client/util/util-gtk.vala
+++ b/src/client/util/util-gtk.vala
@@ -109,12 +109,6 @@ void set_source_color_from_string(Cairo.Context ctx, string spec) {
 }
 
 /**
- * This is not bound in Vala < 0.26.
- */
-[CCode(cname = "g_binding_unbind")]
-extern void unbind(Binding binding);
-
-/**
  * Set xalign property on Gtk.Label in a compatible way.
  *
  * GtkMisc is being deprecated in GTK+ 3 and the "xalign" property has been moved to GtkLabel.  This