The AuditSink resource type (previously in alpha) has been removed
as per https://groups.google.com/g/kubernetes-sig-auth/c/aV_nXpa5uWU.
Remove all support for it from our cainjector so we are able to
continue to upgrade dependencies, and to avoid more users coming
to rely on this functionality ahead of it being removed from
Kubernetes.
Signed-off-by: James Munnelly <james@munnelly.eu>