Remove obsolete --secret-keyring option

Dear keyring maintainers,

Issue

BTS: #1118566

Currently keyring.debian.org lookup with op=get shows:

gpg: WARNING: "--secret-keyring" is an obsolete option - it has no effect

Example: https://keyring.debian.org/pks/lookup?op=get&search=0xD3D7A23522B641FB78ACC775000001EFCF1A50FA

Researches

The related removal code of the secret keyring and its option --secret-keyring in GnuPG was written in 2010.

• Related removal code: https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=commit;h=8e5010a958ded63ab6df89e1ba4d45ed9f2e572a
  • See gnu10/gpg.c: case oSecretKeyring: and others

These removal changes were released at 2014, with GnuPG 2.1.0.

• GnuPG 2.1.0 announcement: https://gnupg.org/faq/whats-new-in-2.1.html#nosecring

Effected versions

The option --secret-keyring was functional up to GnuPG 2.0 (2.0.31 as of 2017-12-30).

It has been ignored since GnuPG 2.1.0 (2014-11-06).

It now triggers a warning in the following versions, due to the fix for upstream bug T2749:

• 2.2.31 <= gnupg < 2.3.0
• 2.3.3 <= gnupg

Therefore, I believe the option --secret-keyring can be safely removed safely if keyring debian.org uses gnupg >= 2.1.0.

Solution

In the commit, I removed --secret-keyring option.