Merge branch 'remove-docs-for-gitlab-ci-service-api' into 'master'

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?

n/a

## Why was this MR needed?

Obsolete information is harmful than nothing.

## What are the relevant issue numbers?

Closes #19167

## Does this MR meet the acceptance criteria?

- [n/a] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [n/a] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4927

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