Re: How do I get rid of a linux system without losing the boot for the others?
My approach would be to boot into Xubuntu and run the command below.
This will update grub with the information from the Xubuntu install; it will still pick up the edubuntu install and add that as an option to the menu.
Next reboot to see if you can get into Xubuntu and Windows without problems. If it works, remove the Edubuntu partition from Windows or Xubuntu, run the above command again in Xubuntu and you should have achieved what you wanted.
As said, that is how I would do it.
And a note: fiddling with disks is always a little risky; user mistakes, power failures, ... I therefore strongly suggest that you have up-to-date backups of anything that is valuable to you, whichever approach you use.
If you don't make backups of your important data, your data is obviously not important to you.