Revert "Ensure immediate canvas update inside GUI windows."

This reverts commit 07f01bd734.

We don't need this anymore as there is now a proper fix
in SimGear.

src/Canvas/window.cxx

@@ -79,17 +79,6 @@ namespace canvas
         _capture_events = node->getBoolValue();
       else
         handled = false;
-
-      // Ensure canvas is redrawn before the window is displayed after it has
-      // been hidden. We can't rely on the cull callback as it gets called too
-      // late (GUI camera is attached as POST_RENDER whereas canvas contents are
-      // rendered during PRE_RENDER).
-      if( node->getNameString() == "visible" && node->getBoolValue() )
-      {
-        simgear::canvas::CanvasPtr canvas = getCanvas().lock();
-        if( canvas )
-          canvas->enableRendering();
-      }
     }
 
     if( !handled )