gpg: Prepare some key cleaning function for use with secret key packets.
* g10/trust.c (mark_usable_uid_certs): Allow use of secret key packets. (clean_sigs_from_uid): Ditto. (clean_uid_from_key): Ditto. (clean_one_uid): Ditto. (clean_key): Ditto.
Since 2.1 secret keys and public keys use identical data structure and
thus we should not restrict those key cleaning functions to work only
with public key packets. This change has no immediate effect but may
come handy in the future.
- Signed-off-by: Werner Koch <wk@gnupg.org>