Remove unused "parent worker global scope" variable

This used to allow setting "the worker's workers", itself used to update the worker's "list of worker's Documents", which doesn't seem to exist anymore.

source

@@ -115963,12 +115963,6 @@ interface <dfn interface>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope
    <li><p>Let <var>owner</var> be the <span>relevant owner to add</span> given <var>outside
    settings</var>.</p></li>
 
-   <li><p>Let <var>parent worker global scope</var> be null.</p>
-
-   <li><p>If <var>owner</var> is a <code>WorkerGlobalScope</code> object (i.e., we are creating a
-   nested dedicated worker), then set <var>parent worker global scope</var> to
-   <var>owner</var>.</p></li>
-
    <li><p>Let <var>unsafeWorkerCreationTime</var> be the <span>unsafe shared current
    time</span>.</p></li>