Remove the worker code IndexCurationWorker

Background

The last step in the process: https://docs.gitlab.com/development/sidekiq/compatibility_across_updates/#removing-worker-classes

This worker is deprecated, not used and just lying in the code

Implementation plan

1. Delete the Search::IndexCurationWorker worker class file
2. Remove reference to class in spec/workers/concerns/search/worker_spec.rb
3. Follow the guidance in our Sidekiq queues documentation around running Rake tasks to regenerate/update related files. Run both rake tasks and commit any changes:

• bin/rake gitlab:sidekiq:all_queues_yml:generate
• bin/rake gitlab:sidekiq:sidekiq_queues_yml:generate