Fix Focal source key deletion

[rmol]

Status

Ready for review

Description of Changes

Fixes #5579.

Adds --yes to gnupg options when deleting source keypairs.

This is the smallest fix, but I also experimented with adding --yes to the options of CryptoUtil.gpg and dispensing with the special GPG instance used in delete_keys, and that works too -- on Focal. On Xenial, with gpg 2.1.11, --pinentry-mode loopback still breaks key deletion.

I read through the mailing list thread linked in the comment in delete_keys and I'm not sure it's still relevant as of gpg 2.2.19, which is what we have on Focal.

So when we drop Xenial, we should be able to drop the extra GPG object too.

Testing

Follow STR from #5579. The source keys should be deleted.

Checklist

If you made changes to the server application code:

• Linting (make lint) and tests (make test) pass in the development container

If you made non-trivial code changes:

• I have written a test plan and validated it for this PR

[kushaldas]

@rmol because dev_focal needs to totally redone, can you please redo the branch against develop by cherry picking the commit? That should fix the lint error.

[kushaldas]

Works as expected, all gpg related tests are now passing on the dev_focal branch.