Remove unused MarginBoxType

Source/core/css/CSSSelector.h

Index: Source/core/css/CSSSelector.h
diff --git a/Source/core/css/CSSSelector.h b/Source/core/css/CSSSelector.h
index 252950ab9aefcaa0cb916a3ed40448b842476148..55c71943b2975ab373fe460f23994a808047b387 100644
--- a/Source/core/css/CSSSelector.h
+++ b/Source/core/css/CSSSelector.h
@@ -203,25 +203,6 @@ public:
         PseudoListBox
     };
 
-    enum MarginBoxType {
-        TopLeftCornerMarginBox,
-        TopLeftMarginBox,
-        TopCenterMarginBox,
-        TopRightMarginBox,
-        TopRightCornerMarginBox,
-        BottomLeftCornerMarginBox,
-        BottomLeftMarginBox,
-        BottomCenterMarginBox,
-        BottomRightMarginBox,
-        BottomRightCornerMarginBox,
-        LeftTopMarginBox,
-        LeftMiddleMarginBox,
-        LeftBottomMarginBox,
-        RightTopMarginBox,
-        RightMiddleMarginBox,
-        RightBottomMarginBox,
-    };
-
     enum AttributeMatchType {
         CaseSensitive,
         CaseInsensitive,