Mark chaos workers as unowned

What does this MR do?

The chaos_engineering category was removed in gitlab-com/www-gitlab-com!47635 (merged)

However, these workers never really belonged to that category anyway, because they're about doing this on the GitLab instance itself: https://docs.gitlab.com/ee/development/chaos_endpoints.html

As they aren't currently used in production, and we don't have any plans to use them soon, it's fine to mark them as unowned.