Skip shipment creation for payment step

https://github.com/openfoodfoundation/openfoodnetwork/issues/2007

Spree 2.0.4 creates in-memory shipments for the payment step. That means
we don't need to create a shipment in that transition. This change
copies the checkout_flow from the Spree code, but leaves one last
customisation: removal of the confirm step.
75ec77dc31

app/models/spree/order_decorator.rb

@@ -30,20 +30,14 @@ Spree::Order.class_eval do
   checkout_flow do
     go_to_state :address
     go_to_state :delivery
-    go_to_state :payment, :if => lambda { |order|
-      # Fix for #2191
-      if order.shipping_method.andand.delivery?
-        if order.ship_address.andand.valid?
-          order.create_shipment!
-          order.update_totals
-        end
-      end
+    go_to_state :payment, if: ->(order) {
+      order.update_totals
       order.payment_required?
     }
     # NOTE: :confirm step was removed because we were not actually using it
     # go_to_state :confirm, :if => lambda { |order| order.confirmation_required? }
     go_to_state :complete
-    remove_transition :from => :delivery, :to => :confirm
+    remove_transition from: :delivery, to: :confirm
   end
 
   # -- Scopes