* scd/app-help.c (app_help_pubkey_from_cert): New.
* scd/command.c (cmd_readkey): Refactor to use that new function and
handle the --advanced flag only here.
* scd/app.c (app_readkey): Remove parm advanced.
* scd/app-common.h (struct app_ctx_s): Remove parm advanced from the
readkey member.
* scd/app-nks.c (do_readkey): Adjust for removed parm.
* scd/app-piv.c (do_readkey): Ditto.
* scd/app-openpgp.c (do_readkey): Ditto.