remove duplicate certificate configuration for proxy test
remove duplicate certificate configuration for proxy test

The issue was introduced in the following commit,
https://github.com/etcd-io/etcd/commit/093282f5eab8b5ba5613b48594aed8794a757c8a

Signed-off-by: Benjamin Wang <a1713d12b1b05630690f22cadfd282d625d8acb2@vmware.com>

etcd-io/etcd,etcd-io/etcd,mqliang/etcd,ajityagaty/etcd,ajityagaty/etcd,etcd-io/etcd,mqliang/etcd,ajityagaty/etcd,mqliang/etcd