Bug#586434: Let's clean the apt cache
> I've done it after you get the "Installation complete" message.
> Can you confirm that this is late enough?
Yes. The last Debian Edu script is at 13debian-edu-profile-udeb
before the installation complete message. The LTSP build is done in
its own udeb between pkgsel and finish-install.
But I would suggest to move it even later, perhaps as late as 60, just
after the backup network setup is done.