Remove ScrollableArea::notifyScrollPositionChanged and cleanup scroll animators.

Source/platform/mac/ScrollAnimatorMac.h

Index: Source/platform/mac/ScrollAnimatorMac.h
diff --git a/Source/platform/mac/ScrollAnimatorMac.h b/Source/platform/mac/ScrollAnimatorMac.h
index 4f91419d8ebe82a46fc5b9b0c5a5504cc02677ad..1c5eb644a55f2e75d9464e0512ddb9dff98fd97e 100644
--- a/Source/platform/mac/ScrollAnimatorMac.h
+++ b/Source/platform/mac/ScrollAnimatorMac.h
@@ -81,7 +81,7 @@ private:
     FloatSize m_contentAreaScrolledTimerScrollDelta;
 
     virtual ScrollResultOneDimensional userScroll(ScrollbarOrientation, ScrollGranularity, float step, float delta) override;
-    virtual void scrollToOffsetWithoutAnimation(const FloatPoint&, ScrollType) override;
+    virtual void scrollToOffsetWithoutAnimation(const FloatPoint&) override;
 
     virtual void handleWheelEventPhase(PlatformWheelEventPhase) override;
 
@@ -116,7 +116,7 @@ private:
 
     FloatPoint adjustScrollPositionIfNecessary(const FloatPoint&) const;
 
-    void immediateScrollTo(const FloatPoint&, ScrollType);
+    void immediateScrollTo(const FloatPoint&);
 
     bool m_haveScrolledSincePageLoad;
     bool m_needsScrollerStyleUpdate;