netdevice: Kill 'feature' test macros.

Almost all of these have long outstayed their welcome.

And for every one of these macros, there are 10 features for which we
didn't add macros.

Let's just delete them all, and get out of habit of doing things this
way.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>