Removing the cargo is the same thing as unloading it, just the world and the date is the same you are currently on. So that method gets called when you click the delete button on a cargo item, or make the jump.
I've also added in the jump process to unload the cargo, and this also automatically adds ship logs for you.
So honestly this is really about 90% done - the UI and a few things need work, but the rest is basically fluff. The core stuff seems to work (of course I say that as the developer without any user testing whatsoever...)