Or if you want to use default Mendix: Loop over List2 and use a find or filter from List1 with the attribute of the iterator in the loop. If it matches remove the found objects from List 1. After the loop you would then have all the objects that do not have a match with List2 in your List1.
Check the appstore for "ListUtils ". That will give you more power over managing your list. Might get you what you need.