netfilter: Get rid of refrences to no longer existant Fast NAT.

Get rid of refrences to no longer existant Fast NAT.

IP_ROUTE_NAT support was removed in August of 2004, but references to Fast
NAT were left in a couple of config options.

Signed-off-by: Russ Dill <Russ.Dill@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>