Merge skipped callback from decorator into model

If we don't want that callback we can just as well remove it now that we
own that code.

app/models/spree/payment.rb

@@ -41,15 +41,6 @@ module Spree
     scope :failed, -> { with_state('failed') }
     scope :valid, -> { where('state NOT IN (?)', %w(failed invalid)) }
 
-    after_rollback :persist_invalid
-
-    def persist_invalid
-      return unless ['failed', 'invalid'].include?(state)
-
-      state_will_change!
-      save
-    end
-
     # order state machine (see http://github.com/pluginaweek/state_machine/tree/master for details)
     state_machine initial: :checkout do
       # With card payments, happens before purchase or authorization happens

app/models/spree/payment_decorator.rb

@@ -1,10 +0,0 @@
-require 'spree/localized_number'
-
-module Spree
-  Payment.class_eval do
-    # 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
-    def persist_invalid; end
-  end
-end