If you don't want to deal with the old save anymore, that's easy enough. Is the save still in the old Sims 3 folder you moved out of Documents? You can delete that entire folder, or just move over the content from that folder that you want, like builds, mods, etc. Here's an explanation of everything in your game folder, so you can decide what you'd like to keep:
https://sims3.crinrict.com/en/2011/01/faq-user-files.html
If you did move the old save to the new game folder, just remove it again. Inside Saves, you'll see a folder labeled .sims3, and, if you moved it as well, another folder labeled .sims3.backup. Remove or trash both copies, and they'll be gone from your game. Or you could just leave them where they are—they won't load or affect your current save while they're sitting there.
By the way, from now on, it's a good idea to periodically use "save as" to rename your current save. This will create a new save with that name and leave the older save file intact. So you'll have plenty of backups in case something goes wrong in the future. I use "save as" at least once a day, and I keep the last 4-6 files and get rid of the earlier backups.