To change or remove the message, simply edit the /etc/motd file in
your favourite text editor either as the root user or using sudo and
then save the file. Clear all the text for no MOTD or replace it with
whatever you would prefer. The next time you log in it will show the
new (or no) text message.

This will work for now, but on reboot the file is reconstructed by
the /etc/init.d/bootmisc.sh script. It writes out "uname -snrvm" to
/var/run/motd (/etc/motd is a symbolic link to /var/run/motd) and then
adds the text from /etc/motd.tail

Therefore to change what goes into the motd file on reboot, edit the
/etc/motd.tail file, making it blank for no message of the day.

If you don’t want the uname information to be included in the motd
file then you would also need to modify the /etc/init.d/bootmisc.sh
file.