remove duplicate findBuildingDef from BuildingSystem

BuildingSystem::findBuildingDef was a byte-equivalent re-implementation of
BuildingsConfig::findBuildingDef. Same cleanup as the GameWorldView copy;
this one sits in the sim layer, so it was missed by both earlier passes.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GH8ZMRY3vhxxXcaUxBqxkk

src/lib/sim/BuildingSystem.h

@@ -267,7 +267,6 @@ private:
     // the status light (REQ-UI-STATUS-LIGHT).
     bool                hasInputsToStart(const Building& b) const;
 
-    const BuildingDef*  findBuildingDef(BuildingType type) const;
     void                initBuffers(Building& b, const RecipeDef& recipe) const;
     // Buffers for an auto-recipe building (Smelter, Reprocessing Plant): input
     // caps span the union of every recipe of the building's type; no player