[css-grid] Drop issue, as WG has agreed with the section.

Author: tabatkins

css-grid/Overview.bs

@@ -2795,8 +2795,6 @@ With a Grid Container as Containing Block</h3>
 	(This happens when both <a>grid-placement properties</a> in an axis contributed a span originally,
 	and [[#grid-placement-errors]] caused the second span to be ignored.)
 
-	Issue: This section is under discussion.
-
 
 <h3 id="static-position">
 With a Grid Container as Parent</h3>