[selectors-4] Fix wording to not imply that specificity of any pseudo-classes depends on matching.

Author: fantasai

selectors-4/Overview.bs

@@ -3265,7 +3265,7 @@ Calculating a selector's specificity</h2>
 	is that of the most specific selector in the list that matches.
 
 	A few pseudo-classes provide “evaluation contexts” for other selectors,
-	and so have their specificity defined by their contents and how they match:
+	and so have their specificity defined specially:
 
 	<ul>
 		<li>