Correct. The effect was originally on during the early days of the ride. The reception was considered too frightening, so it was cut.
The ride has gone through many changes. The reason above is also part of the reason the soul suck dementor no longer has skeleton hands. Also too scary (among some other reasons). The ride motion was also changed at one point to help cut down on people throwing up. In the willow scene, the willow used to whomp a lot harder but it technically entered the ride track. According to an employee I talked to one day, this was okay until one day where the willow didn't whomp back and gave up and the ride was down all day because it was stuck in the track envelope. They most recently changed the floo network supposedly to try and help out with people getting motion sick from being turned and twisted through chimneys.