INFO PGP: openpgp: unsupported feature: S2K function

```
$ kbstage login
▶ WARNING Running in staging mode
Enter a public name for this device: compy
How would you like to sign this install of Keybase?

(1) using PGP (requires access to your PGP key)
Choose a signing option: 1
▶ INFO PGP: openpgp: unsupported feature: S2K function
```

Reproduce the problem with `kbstage login` and the PGP signing option shown in the report. The issue names no files or tests, so first identify the code path handling PGP setup and the S2K error; done should be defined by the maintainers after confirming the intended behavior.

Written by the indexing model from the issue text.