[css-flexbox] Remove paragraph wrt computed values per #644 (WG resolution to compute 'auto' to 'auto' always)

Author: fantasai

css-flexbox/Overview.bs

@@ -2001,12 +2001,7 @@ Cross-axis Alignment: the 'align-items' and 'align-self' properties</h3>
 	If either of the <a>flex item's</a> cross-axis margins are <a value for=margin>auto</a>,
 	'align-self' has no effect.
 
-	On absolutely positioned elements,
-	a value of ''align-self/auto'' computes to itself.
-	On all other elements, a value of <dfn value for=align-self>auto</dfn> for 'align-self'
-	computes to the value of 'align-items' on the element’s parent,
-	or ''align-self/stretch'' if the element has no parent.
-	The alignments are defined as:
+	Values have the following meanings:
 
 	<dl dfn-type=value dfn-for="align-items, align-self">
 		<dt><dfn>flex-start</dfn>