Remove promtail

# Description

Promtail images and helm charts can be removed from the releases, as soon as https://github.com/metal-stack/metal-roles/issues/552 is merged and there was enough time for users to migrate to alloy.

Alloy is introduced in https://github.com/metal-stack/releases/pull/287 and https://github.com/metal-stack/releases/pull/288, this is just a follow-up.