cleanup interfaces for v4

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

service.go

@@ -66,11 +66,6 @@ func RegisterHandler(s server.Server, h interface{}, opts ...server.HandlerOptio
 	return s.Handle(s.NewHandler(h, opts...))
 }
 
-// RegisterSubscriber is syntactic sugar for registering a subscriber
-func RegisterSubscriber(topic string, s server.Server, h interface{}, opts ...server.SubscriberOption) error {
-	return s.Subscribe(s.NewSubscriber(topic, h, opts...))
-}
-
 type service struct {
 	sync.RWMutex
 	opts Options