uploads: switch to active job.

* Switch upload processing from DelayedJob to ActiveJob.
* Remove remaining references to delayed job from tests.

Closes #4128.

test/unit/post_test.rb

@@ -36,17 +36,12 @@ class PostTest < ActiveSupport::TestCase
   context "Deletion:" do
     context "Expunging a post" do
       setup do
-        Delayed::Worker.delay_jobs = true
         @upload = UploadService.new(FactoryBot.attributes_for(:jpg_upload)).start!
         @post = @upload.post
         Favorite.add(post: @post, user: @user)
         create(:favorite_group).add!(@post.id)
       end
 
-      teardown do
-        Delayed::Worker.delay_jobs = false
-      end
-
       should "delete the files" do
         assert_nothing_raised { @post.file(:preview) }
         assert_nothing_raised { @post.file(:original) }