Remove obviously private methods from the public interface in CartService

These methods are not called from anywhere in the app, only in a couple of tests in cart_service_spec.

app/services/cart_service.rb

@@ -22,6 +22,8 @@ class CartService
     valid?
   end
 
+  private
+
   def attempt_cart_add_variants(variants_data)
     loaded_variants = indexed_variants(variants_data)
 
@@ -71,8 +73,6 @@ class CartService
     end
   end
 
-  private
-
   def scoper
     @scoper ||= OpenFoodNetwork::ScopeVariantToHub.new(@distributor)
   end