Remove ScrollableArea::handleGestureEvent

Remove ScrollableArea::handleGestureEvent
https://bugs.webkit.org/show_bug.cgi?id=78661

Reviewed by Sam Weinig.

ScrollableArea::handleGestureEvent ends up being a no-op so remove it and the related code.

* page/EventHandler.cpp:
(WebCore::EventHandler::handleGestureEvent):
* platform/ScrollAnimator.cpp:
* platform/ScrollAnimator.h:
(ScrollAnimator):
* platform/ScrollView.cpp:
(WebCore::ScrollView::wheelEvent):
* platform/ScrollView.h:
(ScrollView):
* platform/ScrollableArea.cpp:
* platform/ScrollableArea.h:
(ScrollableArea):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107774 268f45cc-cd09-0410-ab3c-d52691b4dbfc