[css-syntax-3][editorial] fix diagram. closes #13214

Author: tabatkins

css-syntax-3/Overview.bs

@@ -751,7 +751,7 @@ Token Railroad Diagrams</h3>
 		<dt id="CDO-token-diagram"><<CDO-token>>
 		<dd>
 			<pre class='railroad'>
-			T: <<!---->!--
+			T: <!--
 			</pre>
 
 		<dt id="CDC-token-diagram"><<CDC-token>>