netfilter: nft_set_pipapo: merge deactivate helper into caller

Its the only remaining call site so there is no need for this to
be separated anymore.

Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>