dialog: Remove incorrect disconnectObject()

It was added, as there was a previous signal disconnect in this
function, but it happened to be dead code, and the disconnectObject()
call was added in error. Remove it.

Fixes: 26235bbe54
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1349>

js/ui/dialog.js

@@ -60,8 +60,6 @@ class Dialog extends St.Widget {
     }
 
     makeInactive() {
-        this._parentActor.disconnectObject(this);
-
         this.buttonLayout.get_children().forEach(c => c.set_reactive(false));
     }