Move new Issue relations to EE namespace

app/models/ee/issue.rb

 module EE
   module Issue
+    extend ActiveSupport::Concern
+
+    prepended do
+      has_many :referenced_issue_links, class_name: 'IssueLink', foreign_key: :source_id, dependent: :destroy
+      has_many :referred_by_issue_links, class_name: 'IssueLink', foreign_key: :target_id, dependent: :destroy
+      has_many :referenced_issues, through: :referenced_issue_links, source: :target
+      has_many :referred_by_issues, through: :referred_by_issue_links, source: :source
+    end
+
     # override
     def check_for_spam?
       author.support_bot? || super

app/models/issue.rb

@@ -35,12 +35,6 @@ class Issue < ActiveRecord::Base
   has_many :issue_assignees
   has_many :assignees, class_name: "User", through: :issue_assignees
 
-  has_many :referenced_issue_links, class_name: 'IssueLink', foreign_key: :source_id, dependent: :destroy
-  has_many :referred_by_issue_links, class_name: 'IssueLink', foreign_key: :target_id, dependent: :destroy
-
-  has_many :referenced_issues, through: :referenced_issue_links, source: :target
-  has_many :referred_by_issues, through: :referred_by_issue_links, source: :source
-
   validates :project, presence: true
 
   scope :in_projects, ->(project_ids) { where(project_id: project_ids) }