Update use of Web IDL "invoke a callback function"

The single use, in mutation observers, no longer needs to deal with reporting the exception itself, but simply request that Web IDL do so.

Part of whatwg/webidl#1425.

dom.bs

@@ -3658,8 +3658,8 @@ run these steps:
    <var>mo</var> from <var>node</var>'s <a>registered observer list</a>.
 
    <li><p>If <var>records</var> <a for=queue>is not empty</a>, then <a spec=webidl>invoke</a>
-   <var>mo</var>'s <a for=MutationObserver>callback</a> with « <var>records</var>, <var>mo</var> »,
-   and <var>mo</var>. If this throws an exception, catch it, and <a>report the exception</a>.
+   <var>mo</var>'s <a for=MutationObserver>callback</a> with « <var>records</var>, <var>mo</var> »
+   and "<code>report</code>", and with <a>callback this value</a> <var>mo</var>.
   </ol>
 
  <li><p><a for=set>For each</a> <var>slot</var> of <var>signalSet</var>, <a>fire an event</a> named