gpg: Split key cleaning function for clarity.

* g10/key-clean.c (clean_key): Rename to clean_all_uids and split
subkey cleaning into ...
(clean_all_subkeys): new.  Call that always after the former clean_key
invocations.

Note that the clean_all_subkeys function will later be extended.

(cherry picked from commit 6c3567196f7e72552f326ce07dccbcce31926e5d)

• Signed-off-by: Werner Koch <wk@gnupg.org>