I'd chunk it, if there were no plans to reinstall it, I mean really, even though there's many XP users still around, very few are using 64 bit XP today, or even when released. But read my post before proceeding. Both of your XP's are obviously on the same partition, or whomever did the install was sloppy & didn't cleanup. I'd say both, because you had to make space for Linux Mint. XP Pro would have been the first partition, as it was there before XP Home is. Secondly, GParted would show two partitions for Windows, if they were separate.
This isn't always an easy fix & comes with risk. Not for Linux Mint, it should reboot. But for your XP Home install, doing the wrong thing may render it unbootable. And regardless, you may need your install media for XP Home. You can likely delete all of the XP Pro folders & be OK. It's the removal of the bootloader that may be the issue.
Before I advise further, you'll need to boot into your XP Home partition. If you have a partitioning tool installed, open it, what does it say? XP Home has to be on the "C" partition" Or it will show when you select "Computer" from the Start Menu. I've see this issue before a couple of times when one deleted the Windows 7 partition & installed Linux Mint w/out cleaning up first. Both times, Windows 7 would show as a boot entry & an "Earlier Version of Windows", which was XP. In both cases, the bcdedit menu wasn't cleaned up. This can be tricky, because you have to know the UUID of each & know for sure you're deleting the right one. And in both cases, I refused to touch these, as I had no idea of who did the work. I know what I would have done before deleting those Windows 7 partitions. Gone into msconfig & made XP the first OS to boot into & reboot (one has to if changes are made). This would have "freed" the Windows 7 bootloader, to make formatting the OS easy & that bootloader wouldn't have shown again.
And from there, it's possible that XP Home may not boot. Because it was installed second & not first. I don't even know 100% that a repair "in place" install of XP Home will get rid of this. What this does is keeps all of your folders & installed apps, but you'll have to activate/update XP again.
So from here, I suggest you allow some feedback to flow in as to what to do, as I don't want to be the one who advises you wrong (this UUID stuff can be tricky & as I stated, XP Pro was the first one). Or live with it, if you either cannot get advice on how to purge these XP Pro files & remnant bootloader safely. Again, your XP Home install CD & COA will be needed. THe COA can be found through the Speccy app or Belarc Advisor. If it shows two keys, write both down. Did whomever do the install place a new XP Home COA on the bottom of the notebook? That may be helpful, but not guaranteed, if you can't get up with who installed it. That's why I say, you need your XP Home COA (the key).
I know this sounds like a royal pain in the backside & that's because it is. It all boils down to if you want to put up with a minor detail or not & if not, be prepared for hours of work.
It may be that you can safely delete those XP Pro folders & gain space, but again I cannot promise that. Though if you keep this Topic open, you may generate some positive responses. My guess is that you can delete these, but would like for someone to vouch for it. I've see a few things in my days, but not two installs of XP on the same unformatted partition (if it were formatted, the contents would be gone). I don't understand, why your friend took the easy way out. I've never, ever installed an OS (except in-place repair installs) & not format the partition. That would have been better for your now existing XP Home install also. Formatting gets rid of all the leftovers, including possible infections, and also checks for bad blocks, if not too bad, can repair these.
My techie friend could not fix it so set it aside and installed XP Home Edition.
From what I'm reading, am not so sure of his technical skills. Even you know that when installing Linux Mint, the partitions needs to be formatted. This is an elementary procedure prior to installing any OS. It's my hope that you don't allow whomever this person is to do anymore OS installing, or for that matter, any more computer work for you. Google is your friend, you could have found a good guide & copied it.
I say keep the Topic alive & see how it goes for a few more days. You need to decide on which Linux version to install, so that provides some time.
Thing is, this Topic is in the "Am I Infected" section & I'm not free to advise you on creating a new Topic on this matter. It's in the hands of the Malware Response Team as to what to do next & this being the case, you cannot jump all over the forum for advise on the same issue.
I do hope for a good outcome on this & know what I'd do, given the situation, but your Topic being here places constraints on what you can do.