[css-lists] Remove the special handling of unknown <counter-style> in list-style-type.

Author: tabatkins

css-lists/Overview.bs

@@ -158,9 +158,7 @@ Default Marker Contents: The 'list-style-image' and 'list-style-type' properties
 
 		<dt><dfn>&lt;counter-style></dfn>
 		<dd>
-			If there is a counter style defined matching the <<counter-style>>,
-			the list item's marker's <i>default contents</i> are that counter style. [[CSS-COUNTER-STYLES-3]]
-			Otherwise, the list item's marker's <i>default contents</i> are ''none''.
+			The list item's marker's <i>default contents</i> are that counter style. [[CSS-COUNTER-STYLES-3]]
 
 		<dt><dfn>none</dfn>
 		<dd>