Railskulker Mission vs Buildings expanded

[Levedis]

The Mission "Railskulker_Missions.txt::railskulker_column_4::g_greatest_city_in_the_dwarovar" currently checks for specific buildings to be present. Those Buildings can be upgraded to higher levels thanks to Buildings Expanded which invalidates the mission.
Instead of the basic "has_building = ..." instead use the provided check "province_has_building_of_group = {group = ... all = yes}"

I am pretty sure that some such Problems will pop up every time a new mission update comes from Anbennar.