[css-overflow] Synchronize level 3 and 4

Remove from level 4 parts that are maintained in level 3,
and from level 3 an issue that has been solved in level 4.

Author: frivoal

css-overflow-3/Overview.bs

@@ -421,17 +421,6 @@ Scrolling Origin, Direction, and Restriction</h3>
 
 	The viewport uses the <a>principal writing mode</a> for these calculations.
 
-	<p class="issue">
-		[[CSS3-MARQUEE]] describes an 'overflow-style' property,
-		but it has not picked up implementation experience
-		that the working group is aware of.
-		Should this document treat 'overflow-style' as a defunct proposal,
-		or should this document describe the 'overflow-style' property
-		and attempt to revive it,
-		despite that implementations have implemented
-		'overflow-x' and 'overflow-y' instead?
-
-
 <h2 id="max-lines">
 Limiting Number of Visible Text Lines: the 'max-lines' property</h2>
 
@@ -490,4 +479,3 @@ Acknowledgments</h2>
 		Steve Zilles,
 		and all the rest of the
 		<a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> community.
-