Revert "netfilter: nft_hash: add map lookups for hashing operations"

A better way to implement this from userspace has been found without
specific code in the kernel side, revert this.

Fixes: b9ccc07e ("netfilter: nft_hash: add map lookups for hashing operations")
Signed-off-by: Laura Garcia Liebana <nevola@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>