[css-content] remove document-url value of content-list

Author: dauwhe

css-content/Overview.bs

@@ -164,7 +164,7 @@ Inserting and replacing content with the 'content' property</h2>
 			Equal to:
 
 			<pre class=prod>
-			[ <<string>> | contents | <<image>> | <<quote>> | ''document-url'' | <<target>> | ''leader()'' ]+
+			[ <<string>> | contents | <<image>> | <<quote>> | <<target>> | ''leader()'' ]+
 			</pre>
 
 			Replaces the element's contents with oen or more anonymous inline boxes