Remove duplicate CKS nightly workflow (#974)

The llm-d/llm-d repo already runs `Nightly - WVA E2E (CKS)` using the
same reusable workflow, same cluster, and same namespace. This copy has
never passed (30/30 failures) and wastes runner time.

Signed-off-by: Andrew Anderson <andy@clubanderson.com>

Author: clubanderson