traceroute: move from contrib to usr.sbin

traceroute hasn't had a vendor import since 2002, while since then it's
had several significant FreeBSD-specific commits. Since it's unlikely
another vendor import will happen, and to make the merge of traceroute6
into traceroute easier, import traceroute into usr.sbin.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1100