Remove reverseDuration from implicitly animated widgets, since it's ignored. (#35785)

When I added reverseDuration to animation controllers in #32730, I also added it to the implicit animations that Flutter has. However, as @efortuna pointed out to me, it doesn't actually do anything there, since all of the intrinsic animations run forwards, not in the reverse direction, and there's no way to reverse them.

So, this PR removes the reverseDuration argument from the implicit animations to avoid confusion.

Fixes #35769