How do I edit the SSH "last login" message?
Looks like the format of the printed line is compiled into sshd:
[me@risby ~]$ ssh loryLast login: Fri May 23 10:59:01 2014 from 2a01:2c0:e:300:7271:bcff:feac:445a[me@lory ~]$ strings /usr/sbin/sshd | grep -i "last login"Last login: %sLast login: %s from %s
I can't see any config option for changing that either, so you will need to edit the source and recompile.
Edit: In the limiting case, you can find source at http://www.openssh.org. But you don't tell us that you're using OpenSSH, or anything about your platform, so it's hard to be more specific. If it's a Linux system, you would do much better to get the source appropriate to your distro in the usual way, and recompile through your distro-specific mechanisms.
But really, you shouldn't do this at all unless you have an extremely-compelling business reason to do so: you're making a maintenance nightmare for yourself, going to a hand-compiled version of a security-sensitive package.
The last login information is stored in /var/log/wtmp or /var/log/utmp they are binary files. Without looking at the source code for sshd I can't be entirely sure but I would expect that it is retrieving the information from those files using suitable system calls
It seems unlikely you'll find a way to easily change this information it is after all part of the users security.
If you really want the gory details then you need to look at the source code for the function login_get_lastlog which can be found in loginrec.c
Another solution would be to clear the screen at the beginning of the motd file like so:
^[[H^[[2J
whatever was originally in the motd file here
Note: replace ^[ with the escape symbol (which you can create in the nano editor by pressing the following keys: esc+v+esc)