remove group notation from scroll-start-target (#11147)

Author: keithamus

css-scroll-snap-2/Overview.bs

@@ -167,7 +167,7 @@ Initial scroll target</h4>
 
 	<pre class="propdef">
 		Name: scroll-start-target
-		Value: [ none | auto ]
+		Value: none | auto
 		Initial: ''none''
 		Applies to: all elements
 		Inherited: no