Deprecate and turn down data studio GCP billing report

[BenTheElder]

1. It doesn't correctly reflect sustained use discounts
2. We will always have to maintain this versus the built-in billing reports
3. If we fix https://github.com/kubernetes/k8s.io/issues/4981 we can just grant people access to browse our infra (minus sensitive logs/secrets), billing included
4. We don't have the equivalent for any other vendor, instead we open their built in billing pages in the SIG call and we have a weekly report from CNCF via ii.coop folks in #sig-k8s-infra slack channel that covers the high level spend for all vendors we have credits with (even SIG K8s Infra TLs don't have access to Azure billing currently)

/sig k8s-infra