clients: clarify a misleading comment
clients: clarify a misleading comment

It's clear that client-sets contain many versions of one group, so this
comment just seems to be out-dated.

Signed-off-by: Steve Kuznetsov <skuznets@redhat.com>

Kubernetes-commit: 588f016c3bc04ea2da85d7077643677028a8cb1b

kubernetes/sample-controller,kubernetes/sample-controller