[selectors-4] Remove issue.

Author: fantasai

selectors/Overview.bs

@@ -542,8 +542,6 @@ Structure and Terminology</h3>
 	the <a>next-sibling combinator</a> (U+002B, <code>+</code>),
 	and the <a>following-sibling combinator</a> (U+007E, <code>~</code>).
 
-	Issue: Fill in more combinators, if necessary.
-
 	A <dfn export>selector list</dfn> is a comma-separated list of <a>selectors</a>;
 	see <a href="#grouping">Selector Lists</a>.