Convert animation and renderer code to know about BorderImageLength

Source/core/rendering/style/BorderImageLength.h

Index: Source/core/rendering/style/BorderImageLength.h
diff --git a/Source/core/rendering/style/BorderImageLength.h b/Source/core/rendering/style/BorderImageLength.h
index a2b32a7888014a77331d86530f5baa2eca86d5c7..022796c612a2725b8a994b8a8873893c7e5c784f 100644
--- a/Source/core/rendering/style/BorderImageLength.h
+++ b/Source/core/rendering/style/BorderImageLength.h
@@ -63,9 +63,6 @@ public:
 
     double number() const { ASSERT(isNumber()); return m_length.value(); }
 
-    // FIXME: Remove when the conversion to LengthOrMultipleOfBorderWidthBox is complete.
-    Length deprecatedUnifiedLength() const { return m_length; }
-
     bool operator==(const BorderImageLength& other) const
     {
         return m_length == other.m_length;