[css-color-4] Remove awkward overspecification of GrayText.

Author: tabatkins

css-color-4/Overview.bs

@@ -759,7 +759,7 @@ CSS System Colors</h3>
 		<dd>Text on push buttons.
 
 		<dt><dfn>GrayText</dfn>
-		<dd>Grayed (disabled) text. This color is set to #000 if the current display driver does not support a solid gray color.
+		<dd>Disabled text. (Often, but not necessarily, gray.)
 	</dl>
 
 	Earlier versions of CSS defined additional <<system-color>>s,