libpod: allow cgroup path without infra container

a pod can use cgroups without an infra container.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

libpod/pod.go

@@ -361,9 +361,6 @@ func (p *Pod) CgroupPath() (string, error) {
 	if err := p.updatePod(); err != nil {
 		return "", err
 	}
-	if p.state.InfraContainerID == "" {
-		return "", fmt.Errorf("pod has no infra container: %w", define.ErrNoSuchCtr)
-	}
 	return p.state.CgroupPath, nil
 }