Remove support for Windows Server 2004, 20H2 images

Overview

• Windows Server, version 2004, ended support on 2021-12-14.
• Windows Server, version 20H2, ended support on 2022-08-09.

According to our support policy we should be able to remove support for these since they're no longer maintained by Microsoft.

Proposal

1. Remove references inside GitLab runner code base:
   • Tests
   • Publishing images
   • Helper image selection
2. Remove infrastructure around it
   1. Remove VM image publishing which is used for CI https://gitlab.com/gitlab-org/ci-cd/shared-runners/images/gcp/windows-containers
   2. Remove autoscaler installation in https://ops.gitlab.net/gitlab-com/gl-infra/ci-infrastructure-windows/-/blob/2864ae1b/ansible/group_vars/gcp_role_runner_manager.yml?ref_type=heads#L147-152
   3. Unregister the runners from the gitlab-org/gitlab-runner Settings > CI/Cd > runners section