I installed the Pro Sites 3.5.5 update today and the subscription Cancellation call is no longer sent to Stripes.
Steps to Test:
1) Create a new pro site
2) Click Account -> "Cancel Your Subscription"
3) Log into Stripes and view the logs
The Stripes logs show that a new customer was created along with the associated plan they subscribed to, but a subscription cancellation event was not received.