Clean up Praefect code from deployer and deploy-tooling
Summary
With https://ops.gitlab.net/gitlab-com/gl-infra/deployer/-/merge_requests/593 and https://ops.gitlab.net/gitlab-com/gl-infra/deployer/-/merge_requests/592, we stopped deploying Praefect. See https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/3223 for more details on why this was done.
Proposal
- Remove any remaining code in deployer and deploy-tooling related to Praefect once it is safe to do so.
- Update documentation in https://gitlab.com/gitlab-org/release/docs/.
Edited by Reuben Pereira