Remove ::part.

Source/core/css/CSSTokenizer-in.cpp

Index: Source/core/css/CSSTokenizer-in.cpp
diff --git a/Source/core/css/CSSTokenizer-in.cpp b/Source/core/css/CSSTokenizer-in.cpp
index 3280af1f2967a45c7403dbfb666d93343ea5ff51..001733fcb09c6bf7efd7ba248f5b97ff94adba9c 100644
--- a/Source/core/css/CSSTokenizer-in.cpp
+++ b/Source/core/css/CSSTokenizer-in.cpp
@@ -749,10 +749,6 @@ inline bool CSSTokenizer::detectFunctionTypeToken(int length)
             m_parsingMode = NthChildMode;
             return true;
         }
-        CASE("part") {
-            m_token = PARTFUNCTION;
-            return true;
-        }
     }
     return false;
 }