ssh/key-type.h (key_data): Remove `key_type' field

* ssh/key-type.h (key_data): Remove `key_type' field.
* ssh/key-func.c (guile_ssh_public_key_from_private_key): Update.
* ssh/message-func.c (get_auth_req): Update.
ssh/key-type.h (KEY_TYPE): Remove
ssh/key-type.c (key_types): New structure

* ssh/key-type.h (key_types): Export structure.
* ssh/key-type.c (key_types): New structure.
  (scm_from_ssh_key_type): Use `_ssh_const_to_scm'.
* ssh/key-func.c (key_types): Rename to `hash_types'.
  (guile_ssh_get_public_key_hash): Update.
key-type.h (_ssh_key_type_to_scm, _scm_to_ssh_key_type): New procedures

* ssh/key-type.c (scm_from_ssh_key_type): Rename to
  `_ssh_key_type_to_scm'.  Make it public.
  (_scm_to_ssh_key_type): New procedure.
* ssh/key-type.h (_ssh_key_type_to_scm, _scm_to_ssh_key_type):
  Export.