Remove FREEBSD-vendor files

These files were intended to track version and perhaps maintainership
information for contrib software. However, they were never used beyond
bzip2, netcat, and OpenSSH, and generally haven't been kept up to date
recently (my OpenSSH 8.7p1 update notwithstanding). Just remove them to
avoid having confusing or outdated information.

Suggested by: des
MFC after: 1 week
Sponsored by: The FreeBSD Foundation