[css-color-4][editorial] add dfn attributes to deprecated colors list, fix w3c#9649

Author: svgeesus

css-color-4/Overview.bs

@@ -6512,7 +6512,7 @@ Appendix A: Deprecated CSS System Colors</h2>
 	as the <dfn export><<deprecated-color>></dfn> sub-type,
 	and are defined as:
 
-	<dl noexport>
+	<dl dfn-type="value" dfn-for="<deprecated-color>">
 		<dt><dfn>ActiveBorder</dfn>
 		<dd>Active window border. Same as ''ButtonBorder''.