Get rid of background-clip:text and PaintBehaviorForceBlackText.

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 c5ddf956737b6eebc174592a659c11b40c5d886c..34c26fdd8ec841db9960b3170ada889ba0a4e2ad 100644
--- a/sky/engine/core/css/CSSPrimitiveValueMappings.h
+++ b/sky/engine/core/css/CSSPrimitiveValueMappings.h
@@ -348,9 +348,6 @@ template<> inline CSSPrimitiveValue::CSSPrimitiveValue(EFillBox e)
     case ContentFillBox:
         m_value.valueID = CSSValueContentBox;
         break;
-    case TextFillBox:
-        m_value.valueID = CSSValueText;
-        break;
     }
 }
 
@@ -367,8 +364,6 @@ template<> inline CSSPrimitiveValue::operator EFillBox() const
     case CSSValueContent:
     case CSSValueContentBox:
         return ContentFillBox;
-    case CSSValueText:
-        return TextFillBox;
     default:
         break;
     }