As far as the official AAMC guide to the MCAT is concerned, periodic motion is still on the exam. They specifically mention amplitude, frequency and phase. They also specifically call out the equation for potential energy in springs. This is all under topic 4A. Both springs and pendulums fits the concept of periodic motion, and have been used before. With their new focus, I would doubt that they use spring or pendulums directly as often as they used to, but it very easy to model knee drop tests and muscle loading as pendulums and springs, respectively.
tl, dr: It is still too soon to know HOW they will test periodic motion, but the AAMC has named periodic motion and Spring explicitly as testable topics.