[NET]: Eliminate unused /proc/sys/net/ethernet

The /proc/sys/net/ethernet directory has been sitting empty for more than
10 years!  Time to eliminate it!

Signed-off-by: Jes Sorensen <jes@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>