Remove ElasticIndexingControlWorker class and related files
Description
This removes the ElasticIndexingControlWorker class and related files. It's the last merge request removing the worker.
- %17.9 Remove any code that enqueues the jobs !178182 (merged)
- %17.10 Add a migration that uses sidekiq_remove_jobs !181668 (merged)
- %17.11 Delete the worker class file and related files -> We are here
Reference: https://docs.gitlab.com/development/sidekiq/compatibility_across_updates/#removing-worker-classes
Related to #505250 (closed).