[12.0] GitLab CI features to deprecate and/or remove

Similar to the runner version of this issue, this issue keep tracks of deprecation and removal for %12.0.

Deprecated parts of code should be marked with a // TODO: Remove in 12.0 comment in in the code, and then should be added to the list bellow.

We should ensure that the deprecation was mentioned in both release post and GitLab CE's CHANGELOG.md before %12.0. In %12.0 we should go through the whole list and finally remove all deprecated parts of code.

To Deprecate

To Remove

• Remove kubernetes: active pipeline build policy https://gitlab.com/gitlab-org/gitlab-ce/issues/52148
  • Post deprecation message in release blog post - [link to www-gitlab-com MR]
  • Add deprecation message to the changelog - [link to gitlab-runner MR]
  • Remove deprecated code: [link to gitlab-runner MR]