netfilter: h323: Remove unused function declarations

Commit f587de0e ("[NETFILTER]: nf_conntrack/nf_nat: add H.323 helper port")
declared but never implemented these.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Signed-off-by: Florian Westphal <fw@strlen.de>