netfilter: nf_conncount: remove wrong condition check routine

All lists that reach the tree_nodes_free() function have both zero
counter and true dead flag. The reason for this is that lists to be
release are selected by nf_conncount_gc_list() which already decrements
the list counter and sets on the dead flag. Therefore, this if statement
in tree_nodes_free() is unnecessary and wrong.

Fixes: 31568ec0 ("netfilter: nf_conncount: fix list_del corruption in conn_free")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>