[css-view-transitions-2] Stop extending CSSRule with obsolete pattern (#10607)

Fixes #10606

Author: nt1m

css-view-transitions-2/Overview.bs

@@ -433,14 +433,6 @@ Note: this needs to be cached in the boolean because the result needs to be read
 
 ### Accessing the ''@view-transition'' rule using CSSOM ### {#cssom}
 
-The <code>CSSRule</code> interface is extended as follows:
-
-<pre class='idl'>
-partial interface CSSRule {
-	const unsigned short VIEW_TRANSITION_RULE = 15;
-};
-</pre>
-
 The {{CSSViewTransitionRule}} represents a ''@view-transition'' rule.
 
 <xmp class=idl>
@@ -1025,4 +1017,4 @@ this still presents two potential threats:
 
 See <a href="https://github.com/w3c/csswg-drafts/issues/8684">Issue #8684</a> and
 <a href="https://github.com/WICG/view-transitions/issues/200">WICG/view-transitions#200</a> for
-detailed discussion.
+detailed discussion.