No longer remove tasks for document.open()

This is not consistently implemented and given that Firefox does not appear to do it at all I hope we can get away without it.

Tests: web-platform-tests/wpt#10818.

source

@@ -90644,11 +90644,6 @@ document.body.appendChild(frame)</pre>
    <li><p>For each <span>shadow-including inclusive descendant</span> <var>node</var> of
    <var>document</var>, <span>remove all event listeners</span> with <var>node</var>.</p></li>
 
-   <li><p>Remove any <span data-x="concept-task">tasks</span> associated with <var>document</var> in
-   any <span>task source</span>.</p></li>
-   <!-- removes callbacks that fired between this algorithm starting and the times and databases
-        being aborted in the "unload" step above -->
-
    <li><p><span data-x="concept-node-replace-all">Replace all</span> with null within
    <var>document</var>, without firing any mutation events.</p></li>