src: drop 'virtual' from functions marked 'final' or 'override'

Change-Id: Ieb6df864ab82f77b2bee9e83aa0bfa2005715950
Refs: #3857
diff --git a/src/util/notification-subscriber.hpp b/src/util/notification-subscriber.hpp
index bc7345c..9b86fe1 100644
--- a/src/util/notification-subscriber.hpp
+++ b/src/util/notification-subscriber.hpp
@@ -190,13 +190,13 @@
   signal::Signal<NotificationSubscriber, Notification> onNotification;
 
 private:
-  virtual bool
+  bool
   hasSubscriber() const override
   {
     return !onNotification.isEmpty();
   }
 
-  virtual bool
+  bool
   decodeAndDeliver(const Data& data) override
   {
     Notification notification;