clarified code example: removed unnecessary button type (#38157)

The code example was misleading (Exhibit A: I was misled by it). How so:
- The button type attribute is known to carry behavior w.r.t. its ancestor element (button.type=submit will submit a <form> etc. ; see https://developer.mozilla.org/en-US/docs/Web/HTML/Element/button#type )
- The documentation page is all about closing a <dialog> and raising the cancel event.
- The presence of a <button type="reset"> in the example suggests that the type attribute does actually contribute to the button behavior w.r.t. the <dialog>
- but it does nothing, the closing of the dialog is only the result of a click listener attached via script

files/en-us/web/api/htmldialogelement/cancel_event/index.md

@@ -36,7 +36,7 @@ A generic {{domxref("Event")}}.
 
 ```html
 <dialog class="example-dialog">
-  <button class="close" type="reset">Close</button>
+  <button class="close">Close</button>
 </dialog>
 
 <button class="open-dialog">Open dialog</button>