Move method to more generic helper to use it in mailers

app/helpers/admin/orders_helper.rb

@@ -9,9 +9,5 @@ module Admin
         adjustment.originator_type == "Spree::ShippingMethod"
       end
     end
-
-    def last_payment_method(order)
-      OrderPaymentFinder.new(order).last_payment&.payment_method
-    end
   end
 end