vxge: remove deprecated syststamp timestamp

This driver explicitly clears a field that is unused and about to be
removed. Remove the initialization.

All fields in skb_shared_info before dataref are cleared in
__alloc_skb, so the removal is safe even while syststamp exists.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>