Remove portsnap from HEAD

[bofh]

Summary

portmgr has finally decided to kill portsnap from base on HEAD. Due to this we have also resurrected the old port ports-mgmt/portsnap.

After the EOL of 13 portsnap servers should also be decommissioned from the cluster.

[diizzy]

Thanks for working on this

[bofh]

Committed at https://cgit.freebsd.org/src/commit/?id=df53ae0fdd98e9452095ac2fdaf95fcfac8c9c7f