[NETFILTER]: ctnetlink: remove impossible events tests for updates

IPCT_HELPER and IPCT_NATINFO bits are never set on updates.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>