Remove backface visibility

sky/engine/core/css/CSSPrimitiveValueMappings.h

Index: sky/engine/core/css/CSSPrimitiveValueMappings.h
diff --git a/sky/engine/core/css/CSSPrimitiveValueMappings.h b/sky/engine/core/css/CSSPrimitiveValueMappings.h
index aa67a7144e5c0d2b5119334ded134037b922f817..785b56b78a9716afddb073d0ad0f40702962f4c8 100644
--- a/sky/engine/core/css/CSSPrimitiveValueMappings.h
+++ b/sky/engine/core/css/CSSPrimitiveValueMappings.h
@@ -267,37 +267,6 @@ template<> inline CSSPrimitiveValue::operator CompositeOperator() const
     return CompositeClear;
 }
 
-template<> inline CSSPrimitiveValue::CSSPrimitiveValue(EBackfaceVisibility e)
-    : CSSValue(PrimitiveClass)
-{
-    m_primitiveUnitType = CSS_VALUE_ID;
-    switch (e) {
-    case BackfaceVisibilityVisible:
-        m_value.valueID = CSSValueVisible;
-        break;
-    case BackfaceVisibilityHidden:
-        m_value.valueID = CSSValueHidden;
-        break;
-    }
-}
-
-template<> inline CSSPrimitiveValue::operator EBackfaceVisibility() const
-{
-    ASSERT(isValueID());
-    switch (m_value.valueID) {
-    case CSSValueVisible:
-        return BackfaceVisibilityVisible;
-    case CSSValueHidden:
-        return BackfaceVisibilityHidden;
-    default:
-        break;
-    }
-
-    ASSERT_NOT_REACHED();
-    return BackfaceVisibilityHidden;
-}
-
-
 template<> inline CSSPrimitiveValue::CSSPrimitiveValue(EFillAttachment e)
     : CSSValue(PrimitiveClass)
 {