[css-values-4] Simplify wording

Author: fantasai

css-values-4/Overview.bs

@@ -1165,7 +1165,7 @@ URL Processing Model</h4>
 			with [=fetch/processresponseconsumebody=] set to |processResponse|.
 	</div>
 
-	When interpreting [=URLs=] expressed as CSS <<string>> or <<url>> values,
+	When interpreting [=URLs=] expressed in CSS,
 	the [=URL parser's=] <var ignore>encoding</var> argument
 	must be omitted
 	(i.e. use the default, UTF-8),