Remove some dead code from rendering/ folder

Source/core/rendering/RenderRubyBase.cpp

Index: Source/core/rendering/RenderRubyBase.cpp
diff --git a/Source/core/rendering/RenderRubyBase.cpp b/Source/core/rendering/RenderRubyBase.cpp
index e32478ed14bb7c218de4b2e694f4232101f3d74f..8d9c9ad1c369c4408d77980d060d0153f53cd28a 100644
--- a/Source/core/rendering/RenderRubyBase.cpp
+++ b/Source/core/rendering/RenderRubyBase.cpp
@@ -130,14 +130,6 @@ void RenderRubyBase::moveBlockChildren(RenderRubyBase* toBase, RenderObject* bef
     moveChildrenTo(toBase, firstChild(), beforeChild);
 }
 
-RenderRubyRun* RenderRubyBase::rubyRun() const
-{
-    ASSERT(parent());
-    ASSERT(parent()->isRubyRun());
-
-    return toRenderRubyRun(parent());
-}
-
 ETextAlign RenderRubyBase::textAlignmentForLine(bool /* endsWithSoftBreak */) const
 {
     return JUSTIFY;