I'm not going to contact someone who explicitly said I don't need to keep in touch
What is the reason why you don't want to stay in touch with that person?
I hate having to spend time with negative people.
I think you shouldn't take their words literally - they might have just meant that you don't need to call each other all the time. If you cut them out right now, you might be missing out on a good friendship.
No I'm not wasting my time with that negativity.
Someone might say something and not mean it to be taken literally. Open lines of communication is a good thing, even if you don't talk often. You should just keep their number just in case.