Fix background jobs not using locks like they are supposed to (#13361)

Also:

- Fix locks not being removed when jobs go to the dead job queue
- Add UI for managing locks to the Sidekiq dashboard
- Remove unused Sidekiq workers

Fix #13349

spec/services/import_service_spec.rb

@@ -91,10 +91,6 @@ RSpec.describe ImportService, type: :service do
 
     let(:csv) { attachment_fixture('mute-imports.txt') }
 
-    before do
-      allow(NotificationWorker).to receive(:perform_async)
-    end
-
     describe 'when no accounts are followed' do
       let(:import) { Import.create(account: account, type: 'following', data: csv) }
       it 'follows the listed accounts, including boosts' do
@@ -135,10 +131,6 @@ RSpec.describe ImportService, type: :service do
 
     let(:csv) { attachment_fixture('new-following-imports.txt') }
 
-    before do
-      allow(NotificationWorker).to receive(:perform_async)
-    end
-
     describe 'when no accounts are followed' do
       let(:import) { Import.create(account: account, type: 'following', data: csv) }
       it 'follows the listed accounts, respecting boosts' do