atm: remove commented out check

This preprocessor check is commented out ever since this file was added
during the v2.3 development cycle. It is unclear what it purpose might
have been. Whatever it was, it can safely be removed now.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>