move multiple_issue_boards method from namespace model to group model

app/assets/javascripts/boards/components/board_new_issue.vue

@@ -140,4 +140,3 @@ export default {
     </div>
   </div>
 </template>
-

config/routes/group.rb

@@ -80,7 +80,6 @@ constraints(GroupUrlConstrainer.new) do
     end
 
     resources :billings, only: [:index]
-
     resources :epics do
       member do
         get :realtime_changes

ee/app/models/ee/group.rb

@@ -5,6 +5,7 @@ module EE
   # and be included in the `Group` model
   module Group
     extend ActiveSupport::Concern
+    extend ::Gitlab::Utils::Override
 
     included do
       has_many :epics
@@ -61,5 +62,10 @@ module EE
     def project_creation_level
       super || ::Gitlab::CurrentSettings.default_project_creation
     end
+
+    override :multiple_issue_boards_available?
+    def multiple_issue_boards_available?
+      feature_available?(:multiple_group_issue_boards)
+    end
   end
 end

ee/app/models/ee/namespace.rb

@@ -160,11 +160,6 @@ module EE
       actual_plan&.pipeline_size_limit.to_i
     end
 
-    override :multiple_issue_boards_available?
-    def multiple_issue_boards_available?
-      feature_available?(:multiple_group_issue_boards)
-    end
-
     private
 
     def validate_plan_name