This commit updates the minio/kes-go dependency
to v0.2.0 and updates the existing code to work
with the new KES APIs.
The `SetPolicy` handler got removed since it
may not get implemented by KES at all and could
not have been used in the past since stateless KES
is read-only w.r.t. policies and identities.
Signed-off-by: Andreas Auernhammer <hi@aead.dev>
