openssh: Adjustments after import

- Adjust README.DELETED and README.DRAGONFLY
- Update openbsd-compat
- Regen config.h , adjusting several defines manually because the
configure script seems

openssh: Adjustments after import

- Adjust README.DELETED and README.DRAGONFLY
- Update openbsd-compat
- Regen config.h , adjusting several defines manually because the
configure script seems to not detect everything correctly.
- Add some required source files to SRCS in various programs.

Basic testing done:
- sshd runs and works, i.e. accepts incoming connections, allows different
auth methods (interactive, key).
- X-Forwarding works.
- Can ssh to other OSes.

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Local adjustments for OpenSSH-8.3p1.