jailsetup.sh: replace sshd even if it's busy

jailsetup.sh: replace sshd even if it's busy

Previously if sbin/sshd existed in the jail and was running, then
the attempt to update it would fail.  This can potentially cause
a problem if all the libraries sshd uses are updated in the jail
but the sshd binary itself is not.  The jail could end up with
an older sshd binary that is incompatible with newer libraries.

Avoid this by first removing any existing sshd binary from the
jail before attempting to install sshd.  This will succeed even
if the sshd binary is in use.