OTP releases - 21.2.2 patch & deprecation of < 19

[Dave Cottlehuber]

hey everybody,

FWIW I am just trying out olgeni's steps for bumping 21.2.2 hopefully
it all works fine and we have a few more people able to help out on
regular port bumps.

https://reviews.freebsd.org/D18820 "works for me on amd64"

I also think it's time to deprecate OTP releases 15-18. The OTP team
has already stated that they won't support anything except 20+
which seems pretty reasonable, and anything relying on 19 as a
base that *doesn't* already support 20+ is defacto abandonware.

Thoughts?

A+
Dave