[css-2021] Remove duplicated entry

See w3c#6908

Author: frivoal

css-2021/Overview.bs

@@ -375,12 +375,6 @@ Fairly Stable Modules with limited implementation experience</h3>
 			and adding the ability to specify text emphasis marks
 			and text shadows.
 
-		<dt><a href="https://www.w3.org/TR/css-counter-styles-3/">CSS Counter Styles Level 3</a>
-		  [[CSS-COUNTER-STYLES-3]]
-		<dd>
-			Expands the possible values of <<counter-style>>
-			and provides an ''@counter-style'' syntax for customized counter styles.
-
 		<dt><a href="https://www.w3.org/TR/css-masking-1/">CSS Masking Level 1</a>
 		  [[CSS-MASKING-1]]
 		<dd>