Explicitly use the class name that is being deprecated

The message is otherwise hard to understand.

Author: elia

core/app/models/spree/user_last_url_storer.rb

@@ -26,7 +26,7 @@ def self.rules
     #  or its subclasses. The controller will be passed to each rule for matching.
     def initialize(controller)
       @controller = controller
-      Spree::Deprecation.warn("This class will be removed without replacement on the release of Solidus 4.0")
+      Spree::Deprecation.warn("Spree::UserLastUrlStorer will be removed without replacement on the release of Solidus 4.0")
     end
 
     # Stores into session[:spree_user_return_to] the request full path for