common: Remove openpgp_oid_to_kem_algo.

* common/openpgp-oid.c (oidtable): Don't include kem_algo.
(openpgp_oid_to_kem_algo): Remove.

The information is now retrieved by openpgp_oid_to_curve +
gnupg_get_ecc_params.

• GnuPG-bug-id: T7698
• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>