[css-overflow] Remove 'contain' dependency per WG resolution

Author: fantasai

css-overflow-3/Overview.bs

@@ -232,7 +232,7 @@ Scrollable Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</
 		Inherited: no
 		Percentages: N/A
 		Media: visual
-		Computed value: see below
+		Computed value: as specified, except with ''visible'' computing to ''auto'' if one of 'overflow-x' or 'overflow-y' is not ''visible''
 		Animatable: no
 	</pre>
 
@@ -322,34 +322,8 @@ Scrollable Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</
 	If the computed value of 'overflow' on a <a>block box</a> is not ''overflow/visible'',
 	it creates a new <a>block formatting context</a> for its content.
 
-<h3 id="overflow-computed-values">
-Overflow Value Computation and Propagation</h3>
-
-		<p>The computed values of 'overflow-x' and 'overflow-y'
-		are determined from the <a>specified values</a> [[!CSS3CASCADE]]
-		based on the following rules:
-
-		<ol>
-			<li>
-				If one <a>specified value</a> is ''overflow/visible''
-				and the other is not,
-				then computed values are the <a>specified values</a>
-				with ''overflow/visible'' changed to ''overflow/auto''.
-			</li>
-			<li>
-				Otherwise, if both <a>specified values</a> are ''overflow/visible''
-				and the computed value of 'contain' is
-				one that activates <a>paint containment</a>
-				(e.g. ''contain:strict''
-				or ''contain: paint''
-				or ''contain: layout paint''…),
-				then the computed values of both 'overflow-x' and 'overflow-y'
-				are changed to ''overflow/clip''.</li>
-			<li>
-				Otherwise, the computed values are as specified.
-			</li>
-		</ol>
-	</div>
+<h3 id="overflow-propagation">
+Overflow Value Propagation</h3>
 
 	UAs must apply the 'overflow' property
 	set on the root element to the viewport.