* common/util.h (gnupg_ecc_kem_kdf): Change the last two args.
* common/kem.c (gnupg_ecc_kem_kdf): The last arguments are KDF_PARAMS
and its length.
* agent/pkdecrypt.c (composite_pgp_kem_decrypt): Follow the change.
* g10/pkglue.c (do_encrypt_kem): Follow the change.
* g10/ecdh.c (extract_secret_x, derive_kek): Remove.
(gnupg_ecc_6637_kdf): Remove.
(ecc_build_kdf_params): Rename from build_kdf_params, changing
arguments.
* g10/pkglue.c (do_encrypt_ecdh): Refactor by ecc_build_kdf_params and
gnupg_ecc_kem_kdf.
* g10/pkglue.h (pk_ecdh_decrypt, gnupg_ecc_6637_kdf): Remove.
(ecc_build_kdf_params): New.
* g10/pubkey-enc.c (ecdh_sexp_build): Use ecc_build_kdf_params.