There are still some variables and forward declarations in the map-reading C++ code related to the old CTriggerManager class, and the old trigger system (added in rP4648, and then later removed).
A pointer to a CTriggerManager object is passed in every call to LoadMap and LoadRandomMap in World.cpp (and ends up being stored as a member var in CMapReader), but the CTriggerManager class does not actually exist. In MapWriter.h, there is the forward declaration of two structs (MapTrigger and MapTriggerGroup), which can be removed.
Also remove some unneeded includes from World.cpp. (There is some duplicated code in between the two LoadMap/LoadRandomMap chains, but that is for another diff.)