HumbleButton: Remove unused allow free (#2408)

Author: leolost2605

src/Widgets/ActionStack.vala

@@ -129,8 +129,6 @@ public class AppCenter.ActionStack : Gtk.Box {
             }
         }
 
-        action_button.allow_free = true;
-
         if (stack.get_child_by_name ("buttons") != null) {
             stack.visible_child_name = "buttons";
         }
@@ -150,8 +148,6 @@ public class AppCenter.ActionStack : Gtk.Box {
             case AppCenterCore.Package.State.INSTALLED:
                 action_button_revealer.reveal_child = package.should_pay && updates_view;
                 open_button_revealer.reveal_child = show_open && package.get_can_launch ();
-
-                action_button.allow_free = false;
                 break;
             case AppCenterCore.Package.State.UPDATE_AVAILABLE:
                 action_button.free_string = _("Update");

src/Widgets/HumbleButton.vala

@@ -40,18 +40,6 @@ public class AppCenter.Widgets.HumbleButton : Gtk.Button {
 
     public string free_string;
 
-    public bool _allow_free = true;
-    public bool allow_free {
-        get {
-            return _allow_free;
-        }
-        set {
-            if (value != _allow_free) {
-                _allow_free = value;
-            }
-        }
-    }
-
     public bool can_purchase {
         set {
             if (!value) {