yes... you should do a reduction on days off... but thats assuming that your calories are in the right place already..
for example.. if youre cutting at 3000 calories.. you would reduce to 2600 calories by simply removing your post workout nutrition on days you dont work out.. given that your post workout nutrition is correct..
usually post workout nutrition will range between 200-400 calories.. if youre having the correct protein and carb intake post workout removing it will reduce your calories correctly..
again, this is all assumption on a proper diet being used