Add 204. Remove duplicated method.

lib/api/group_variables.rb

@@ -88,6 +88,7 @@ module API
         variable = user_group.variables.find_by(key: params[:key])
         not_found!('GroupVariable') unless variable
 
+        status 204
         variable.destroy
       end
     end

lib/api/helpers.rb

@@ -33,10 +33,6 @@ module API
       @project ||= find_project!(params[:id])
     end
 
-    def user_group
-      @group ||= find_group!(params[:id])
-    end
-
     def available_labels
       @available_labels ||= LabelsFinder.new(current_user, project_id: user_project.id).execute
     end