jobs: migrate file deletion jobs to ActiveJob.

test/test_helper.rb

@@ -53,8 +53,15 @@ module TestHelpers
       Thread.current[:pixiv_comic_session_cache_key] = Cache.get(PixivWebAgent::COMIC_SESSION_CACHE_KEY)
     end
   end
-end
 
+  # XXX replace with `perform_enqueued_jobs` after rails 6 upgrade.
+  def workoff_active_jobs
+    queue_adapter.enqueued_jobs.each do |job_data|
+      klass = job_data[:job]
+      klass.perform_now(*job_data[:args])
+    end
+  end
+end
 
 class ActiveSupport::TestCase
   include ActiveJob::TestHelper