remove group notation from outline-color (#11053)

Author: keithamus

css-ui-4/Overview.bs

@@ -436,7 +436,7 @@ Outline Colors: the 'outline-color' property</h3>
 
 	<pre class="propdef">
 	Name: outline-color
-	Value: auto | [ <<color>> | <<image-1D>> ]
+	Value: auto | <<color>> | <<image-1D>>
 	Initial: auto
 	Applies to: all elements
 	Inherited: no