isdn: hisax: Drop duplicate Kconfig entry

There are 2 HISAX_AVM_A1_PCMCIA Kconfig entries. The kbuild system
ignores the second one, and apparently nobody noticed the problem so
far, so let's remove that second entry.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Karsten Keil <isdn@linux-pingi.de>
Signed-off-by: David S. Miller <davem@davemloft.net>