Make HTMLHyperlinkElementUtils a mixin, not a NoInterfaceObject

Commit b8afa0a converted several interfaces
from NoInterfaceObject to mixins. It looks like it missed
HTMLHyperlinkElementUtils: it did update the interfaces that use
HTMLHyperlinkElementUtils (from "implements" to "includes"), but did not mark
HTMLHyperlinkElementUtils as a mixin.

Fix it, which makes HtmlAnchorElement gain useful functions like `set_href`.

Author: marienz

crates/web-sys/webidls/enabled/HTMLHyperlinkElementUtils.webidl

@@ -10,8 +10,7 @@
  * and create derivative works of this document.
  */
 
-[NoInterfaceObject]
-interface HTMLHyperlinkElementUtils {
+interface mixin HTMLHyperlinkElementUtils {
   // Bug 824857: no support for stringifier attributes yet.
   //  stringifier attribute USVString href;