I believe that you can remove the HDD from that Macbook fairly easily (certainly an SSD replacement is a standard upgrade), so you could remove the HDD and connect it to a Windows PC using a USB - SATA caddy or interface and run a disk erase utility on it that way. If your brief is simply to remove personal data rather than also provide a working Macbook, just remove the HDD and destroy it, leaving it to the next user to install their preferred disk and Mac OS version, .
SD