[Feature] Remove old addons automatically

[HalalaiMircea]

I updated the script to also remove VPKs that were deleted from the Steam collection.

• Add remove_old_plugins function that finds plugins IDs present in the old list, but not in the new one from Steam API. Removes associated VPK(s) with those IDs
• Remove 2 lines that added old plugin ids to the new list so it doesn't redownload the old ones that were removed from Steam collection