Reviewed by Simon Fraser.

        https://bugs.webkit.org/show_bug.cgi?id=26943

        When one transition finishes slightly before another the longer
        one will fire a second time. This is because the second
        ImplicitAnmation object is culled too early, before its final
        RenderStyle is in place. This is done by cleanupFinishedAnimations()
        so I got rid of that method completely and now cleanup each
        transition or animation at the point where I am setting the final
        style, or when I detect that the transition or animation has been
        terminated early (which happens when you remove it from the style).

        Test: transitions/extra-transition.html

        * page/animation/AnimationController.cpp:
        (WebCore::AnimationControllerPrivate::updateStyleIfNeededDispatcherFired):
        * page/animation/CompositeAnimation.cpp:
        (WebCore::CompositeAnimation::updateTransitions):
        (WebCore::C...