Fix an issue with sidekiq starting in docker compose

What does this MR do?

By removing a nil setting that doesn't work with sidekiq-cluster

Related issues

This is a workaround for gitlab-org/gitlab#349143 (closed)

Test steps:

1. Checkout master branch of this project
2. Update your https://gitlab.com/gitlab-org/build/CNG/-/blob/master/.env file and set IMAGE_TAG to 14-6-stable
3. docker-compose pull
4. docker-compose up -d
5. docker-compose logs -f sidekiq

You should see the error.

If you checkout this branch, and follow the same steps, there should be no sidekiq errors

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated