Remove delivery overlays for istio components
What
Remove Delivery tenant values overlay references since the overlays have been migrated to the Reliability tenant on gitlab-com/gl-infra/k8s-mgmt/tenants/reliability!37 (merged)
Why
All Istio components configs should live under the Reliability tenant to make it easier to maintain.
Related Issue: https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/24157