compositor: Clean up comment

So it seems that we were intentionally delaying the output window,
although I wonder why...

src/compositor/compositor.c

@@ -796,13 +796,6 @@ meta_compositor_manage_screen (MetaCompositor *compositor,
     }
   else
     {
-      /*
-       * Delay the creation of the overlay window as long as we can, to avoid
-       * blanking out the screen. This means that during the plugin loading, the
-       * overlay window is not accessible; if the plugin needs to access it
-       * directly, it should hook into the "show" signal on stage, and do
-       * its stuff there.
-       */
       info->output = get_output_window (screen);
       XReparentWindow (xdisplay, xwin, info->output, 0, 0);