As Joan notes, motd is the key. You can change the message to whatever you want by editing the motd file:

sudo pico /etc/motd

If you just want to disable it for your user, create a .hushlogin file in your home directory:

touch ~/.hushlogin

As Joan notes, motd is the key. The Debian wiki has good information on how the motd file is generated at boot and how to modify it. Check out the How to keep your /etc/motd from being overwritten section to make permanent motd changes.

If you just want to disable it for your user, create a .hushlogin file in your home directory:

touch ~/.hushlogin