Replace HiFive 1B since it is discontinued

[deadprogram]

I think we should remove the HiFive 1B board since it has been discontinued for some time. See https://www.sifive.com/boards/hifive1-rev-b

Perhaps we can replace with ESP32-C3 or something?

[aykevl]

Hmm. We can, but it hasn't been a big maintenance burden for me. Feel free to make PRs to remove it though.