[css-color] Remove unused DOMString term from "Ignored Terms".

Author: SimonSapin

css-color/Overview.bs

@@ -13,7 +13,7 @@ Former Editor: L. David Baron, Mozilla Corporation, dbaron@dbaron.org
 Abstract: This specification describes CSS <<color>> values and properties for foreground color and group opacity.
 Repository: w3c/csswg-drafts
 Inline Github Issues: title
-Ignored Terms: stacking context, double, octet, DOMString
+Ignored Terms: stacking context, double, octet
 </pre>
 
 <style>