Take a look at the following two sources:
Online Etymology Dictionary
"to invoke spirits," from Old French exorciser (14c.), from Late Latin exorcizare, from Greek exorkizein "banish an evil spirit; bind by oath”
"condition of being in active operation; practice for the sake of training," from Old French exercice (13c.) "exercise, execution of power; physical or spiritual exercise," from Latin exercitium "training, exercise" (of soldiers, horsemen, etc.); "play;"
So as pointed out, both use the ex prefix but they don’t seem to be very related.
