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

doc/api/services.md

@@ -374,40 +374,6 @@ Get Gemnasium service settings for a project.
 GET /projects/:id/services/gemnasium
 ```
 
-## GitLab CI
-
-Continuous integration server from GitLab
-
-### Create/Edit GitLab CI service
-
-Set GitLab CI service for a project.
-
-```
-PUT /projects/:id/services/gitlab-ci
-```
-
-Parameters:
-
-- `token` (**required**) - GitLab CI project specific token
-- `project_url` (**required**) - http://ci.gitlabhq.com/projects/3
-- `enable_ssl_verification` (optional) - Enable SSL verification
-
-### Delete GitLab CI service
-
-Delete GitLab CI service for a project.
-
-```
-DELETE /projects/:id/services/gitlab-ci
-```
-
-### Get GitLab CI service settings
-
-Get GitLab CI service settings for a project.
-
-```
-GET /projects/:id/services/gitlab-ci
-```
-
 ## HipChat
 
 Private group chat and IM