scd:openpgp: Return key creation time as part of KEYPARIINFO.

* scd/app-openpgp.c (send_keypair_info): Reaturn the key creation time
as part of a KEYPAIRINFO.
(do_readkey): Do not return the KEY-TIME anymore.

Sending the KEY_TIME status as part of a READKEY command was only
recently added. It is better to merge that into the KEYPAIRINFO line.
Another patch with chnage this for the consumers of that info.

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