New Content - Implemented unused prefernce in defaults

Updating a script I noticed that there is still a preferences in defaults.txt which should be removed since they are no longer used: lastHiddenCityAscension. That's particularly amusing since hiddenCityLayout was already removed.

Not a big deal, but hey, might as well. It would be nice if it stopped showing up when I did a prefref.

Darzil removed this with revision 13146