netfilter: nf_nat_snmp_basic: remove debug parameter

To see debug message of nf_nat_snmp_basic, we should set debug value
when we insert this module. but it is inconvenient and only using of
the dynamic debugging is enough to debug.

This patch just removes debug code. then in the next patch, debugging code
will be added.

Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>