[interpreter] `Tls.encodePrivateKey` and `Tls.encodeCert` don't work

[jaredly]

Tls.encodePrivateKey just calls show on the data structure, and actually doesn't return the right type (it returns Text instead of Bytes), so using it results in a run-time type error. And show doesn't produce anything that decodePrivateKey can handle.

Tls.encodeCert looks like it's doing a little better work, but it also doesn't produce bytes that can be handled by decodeCert

[aryairani]

@jaredly Could you attach a transcript.md if this issue is still ongoing?