Extract domain's "delete_time" attribute to deletable concern

app/models/concerns/domain/deletable.rb

@@ -1,6 +1,10 @@
 module Concerns::Domain::Deletable
   extend ActiveSupport::Concern
 
+  included do
+    alias_attribute :delete_time, :delete_at
+  end
+
   def discarded?
     statuses.include?(DomainStatus::DELETE_CANDIDATE)
   end

spec/models/concerns/domain/deletable_spec.rb

@@ -1,6 +1,8 @@
 require 'rails_helper'
 
 RSpec.describe Domain, db: false do
+  it { is_expected.to alias_attribute(:delete_time, :delete_at) }
+
   describe '#discarded?' do
     context 'when :deleteCandidate status is present' do
       let(:domain) { described_class.new(statuses: [DomainStatus::DELETE_CANDIDATE]) }

spec/models/domain_spec.rb

@@ -699,7 +699,6 @@ end
 
 RSpec.describe Domain, db: false do
   it { is_expected.to alias_attribute(:on_hold_time, :outzone_at) }
-  it { is_expected.to alias_attribute(:delete_time, :delete_at) }
   it { is_expected.to alias_attribute(:force_delete_time, :force_delete_at) }
   it { is_expected.to alias_attribute(:outzone_time, :outzone_at) }