gpg: Tweak compliance checking for verification

* common/compliance.c (gnupg_pk_is_allowed): Rework to always allow
verification.
* g10/mainproc.c (check_sig_and_print): Print a con-compliant warning.
* g10/sig-check.c (check_signature2): Use log_error instead of
log_info.

We should be able to verify all signatures. So we only print a
warning. That is the same beheavour as for untrusted keys etc.

• GnuPG-bug-id: T3311
• Signed-off-by: Werner Koch <wk@gnupg.org>