polkitAgent: Fix closing dialog properly

When pressing the close button on the dialog the polkit request isn't
completed leaving the polkit agent blocked unable to handle new
requests.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2761>

js/ui/components/polkitAgent.js

@@ -391,7 +391,6 @@ var AuthenticationDialog = GObject.registerClass({
     }
 
     cancel() {
-        this.close(global.get_current_time());
         this._emitDone(true);
     }