Remove some dead code from rendering/ folder

Source/core/rendering/RenderFlexibleBox.h

Index: Source/core/rendering/RenderFlexibleBox.h
diff --git a/Source/core/rendering/RenderFlexibleBox.h b/Source/core/rendering/RenderFlexibleBox.h
index 5b7ace5ad06957c2d1696b956c341f4d82f75502..053f384807da089e77d0c27037a12935dcbb1651 100644
--- a/Source/core/rendering/RenderFlexibleBox.h
+++ b/Source/core/rendering/RenderFlexibleBox.h
@@ -89,7 +89,6 @@ private:
     bool isLeftToRightFlow() const;
     bool isMultiline() const;
     Length flexBasisForChild(RenderBox* child) const;
-    void setCrossAxisExtent(LayoutUnit);
     LayoutUnit crossAxisExtentForChild(RenderBox* child) const;
     LayoutUnit mainAxisExtentForChild(RenderBox* child) const;
     LayoutUnit crossAxisExtent() const;
@@ -109,7 +108,6 @@ private:
     LayoutUnit flowAwareMarginStartForChild(RenderBox* child) const;
     LayoutUnit flowAwareMarginEndForChild(RenderBox* child) const;
     LayoutUnit flowAwareMarginBeforeForChild(RenderBox* child) const;
-    LayoutUnit flowAwareMarginAfterForChild(RenderBox* child) const;
     LayoutUnit crossAxisMarginExtentForChild(RenderBox* child) const;
     LayoutUnit crossAxisScrollbarExtent() const;
     LayoutPoint flowAwareLocationForChild(RenderBox* child) const;
@@ -118,7 +116,6 @@ private:
     void adjustAlignmentForChild(RenderBox* child, LayoutUnit);
     ItemPosition alignmentForChild(RenderBox* child) const;
     LayoutUnit mainAxisBorderAndPaddingExtentForChild(RenderBox* child) const;
-    LayoutUnit mainAxisScrollbarExtentForChild(RenderBox* child) const;
     LayoutUnit preferredMainAxisContentExtentForChild(RenderBox* child, bool hasInfiniteLineLength, bool relayoutChildren = false);
     bool childPreferredMainAxisContentExtentRequiresLayout(RenderBox* child, bool hasInfiniteLineLength) const;