Make sure we're only calling $panels_display->setStorage() when writing (not reading)

While iterating toward a working Panelizer, we put in some hacks to call $panels_display->setStorage() when reading a Panels display to make sure it had the correct values.

However, this should really only be called before saving the Panels display, not reading it!

We still have some left-over code that does this in Panelizer::getDefaultPanelsDisplay() and possibly elsewhere... Fix this!