To remove all the pre-installed games on ubuntu, run

sudo apt purge gnome-games

sudo apt autoremove

Or in one line:

sudo apt purge --autoremove gnome-games

Ok, so a bit of background I was looking at the package page for ubuntu-desktop and found nothing about games, and then for the fun of it looked up gnome-games and well I found it.

The purge command removes all configs and all packages after it. autoremove removes unneeded packages on your system.