I think it's better to release it, but it depends.
Some PD's will only care about USMLE's. IN that case, they won't care about your COMLEX, and whether you release it or not will not matter.
Some PD's will care about your COMLEX. IN that case, they may see your absence of COMLEX scores as a big red flag.
One option would be to not release them, and then release them on request of PD's. Simply state "as I took the USMLE's, I assumed you would not consider my COMLEX scores. I'll release them today." if asked.
It also depends on your COMLEX scores. If you got a 752 on step 1 and then a 698 on Step 2, no one is going to care and you should simply release them. If you got a 490 on step 1 and then a 422 on Step 2, that's much more of a concern.