You can’t “remove” them they’re built into the entire foundation of discourse they aren’t simply pre-made groups, groups sit on top of them and all groups use the trust level system. But yes you can lock categories to either/both.
You might want to read the Trust Level guide which explains what they do, because any group you make will be reliant on this. A group is just a group of users, all of which have a Trust Level: either static (every member in the group gets the one assigned to the group), or independent where they all have whatever level they’re naturally at.