Remove inheritance from EventTarget for CSSPseudoElement IDL (#13168)

As resolved in #12163
the CSSPseudoElement IDL is not an EventTarget inheritor anymore.

Co-authored-by: Tab Atkins Jr. <jackalmage@gmail.com>

Author: danielsakhapov

css-pseudo-4/Overview.bs

@@ -1786,12 +1786,9 @@ Additions to the CSS Object Model</h2>
 <h3 id="CSSPseudoElement-interface">
 {{CSSPseudoElement}} Interface</h3>
 
-  The {{CSSPseudoElement}} interface
-  allows [=pseudo-elements=] to be event targets.
-
   <pre class="idl">
     [Exposed=Window]
-    interface CSSPseudoElement : EventTarget {
+    interface CSSPseudoElement {
         readonly attribute CSSOMString type;
         readonly attribute Element element;
         readonly attribute (Element or CSSPseudoElement) parent;