[css-containment] Remove explicit spec links after fixing that spec

css-regions now exports its definitions, so we can link to them without
being extra verbose.

Author: frivoal

css-containment/Overview.bs

@@ -156,8 +156,8 @@ Layout Containment</h3>
 		but do not receive any content from the <a>fragmented flow</a>.
 
 		Specifically:
-			- <a spec=css-regions>CSS Regions</a> following the one which traps the content
-				are still considered part of the <a spec=css-regions>region chain</a>
+			- <a>CSS Regions</a> following the one which traps the content
+				are still considered part of the <a>region chain</a>
 				as returned by the {{NamedFlow/getRegions()}} method
 				of the {{NamedFlow}} interface.
 			- the {{regionOverset}} attribute of the {{Region}} interface