[css-values] Revert the 'url(#foo) in an external stylesheet refers to the host document' behavior, per WG resolution.

Author: tabatkins

css-values/Overview.bs

@@ -589,14 +589,10 @@ Fragment URLs</h4>
 
 	When matching a ''url()'' with the <a>local url flag</a> set,
 	ignore everything but the URL's fragment,
-	and resolve that fragment against the host document.
+	and resolve that fragment against the current document that relative URLs are resolved against.
 	This reference must always be treated as same-document
 	(rather than cross-document).
 
-	Note: This means that an SVG reference like ''url(#my-gradient)''
-	will work the same whether the CSS is written inline in the SVG document
-	or linked in as an external CSS stylesheet.
-
 	When serializing a ''url()'' with the <a>local url flag</a> set,
 	it must serialize as just the fragment.