[gnome-usage] primary-menu: remove unused variable, it fix build warning

[Petr Štětka <pstetka src gnome org>]

commit 66616056df11a6b65b613f40cdd60bb9cc46e86e
Author: Petr Štětka <pstetka redhat com>
Date:   Wed Dec 19 14:05:14 2018 +0100

    primary-menu: remove unused variable, it fix build warning

 src/primary-menu.vala | 2 --
 1 file changed, 2 deletions(-)
---
diff --git a/src/primary-menu.vala b/src/primary-menu.vala
index e39668d..2275f17 100644
--- a/src/primary-menu.vala
+++ b/src/primary-menu.vala
@@ -23,8 +23,6 @@ using Gtk;
 namespace Usage {
     [GtkTemplate (ui="/org/gnome/Usage/ui/primary-menu.ui")]
     public class PrimaryMenu : Gtk.Popover {
-        [GtkChild]
-        private Gtk.ModelButton about_usage_button;
 
         [GtkChild]
         private Gtk.Box performance_container;