Removing expiry dates for TOFU

[Solderpunk]

By the way, I appreciate you writing this up, and also your earlier post
on TOFU which you shared here.

I've finally started work on my gentle TLS cert introduction, it's at
gemini://gemini.circumlunar.space/docs/tls-tutorial.gmi.  So far it's
just background stuff, but TOFU will feature eventually.  Keep an eye on
it over the next week or so.  Feedback welcome at any stage, though.

Cheers,
Solderpunk