In order to perform this skip you need a golden key before starting level 19. Then you need to start spamming the attack button in order to deal as much damage to the stone wall as possible, ideally you break it quick enough to pass through before the cut scene starts, if you don't it is up to you whether you want to restart the level or let the cut scene play, the difference is relatively small. You can tell that you got the skip if the screen follows you into the next room, if it does you need to use the golden key to unlock the gate, you can't collect the key from the skeleton because that would put you within range of the cut scene, triggering it.