Remove docs for GitLab CI Service API
What does this MR do?
Documentation update: http://docs.gitlab.com/ce/api/services.html
Old GitLab CI Service API description will be removed from the docs.
Are there points in the code the reviewer needs to double check?
Why was this MR needed?
Obsolete information is harmful than nothing.
What are the relevant issue numbers?
Closes #19167 (closed)