Make the motd generation completely static with this change.
Prepending the output of uname(1) may lead to confusing and/or incorrect
output if you are in a jail which has a different version of world
compared to the jailhost kernel/world. For those who need a fully
dynamic motd can still use sysutils/dynamic_motd port.
PR: 276763
Approved by: jrm (mentor), otis (mentor), emaste
MFC after: 1 month