Move method delegation from decorator to model

app/models/spree/payment.rb

@@ -7,6 +7,8 @@ module Spree
 
     IDENTIFIER_CHARS = (('A'..'Z').to_a + ('0'..'9').to_a - %w(0 1 I O)).freeze
 
+    delegate :line_items, to: :order
+
     belongs_to :order, class_name: 'Spree::Order'
     belongs_to :source, polymorphic: true
     belongs_to :payment_method, class_name: 'Spree::PaymentMethod'

app/models/spree/payment_decorator.rb

@@ -2,8 +2,6 @@ require 'spree/localized_number'
 
 module Spree
   Payment.class_eval do
-    delegate :line_items, to: :order
-
     # We bypass this after_rollback callback that is setup in Spree::Payment
     # The issues the callback fixes are not experienced in OFN:
     #   if a payment fails on checkout the state "failed" is persisted correctly