I did this (took test months before applying and then changed my mind). You don't have to do anything. Generally, schools will link a score report with an application after you initialize one and provide the info necessary to do the link. If you don't submit an application, then the received score report just won't link to anything.
I am not 100% sure but based on some conversations with admissions staff, it sounds like there isn't a physical score report so it's not like anyone needs to manually sort your report somewhere. It's all electronic and goes into a database which only gets linked after an application is created. So if you don't send anything, I'm sure the score report just lives there until it expires (5 years).