drop removeBuilding, which nothing has called for a while

A public mutator that erased a building with no refund and no deconstruction
queue, documented as being "used for deaths". Nothing calls it: stations and the
HQ became ECS entities, so a death releases its tiles through
unregisterTileOccupancy instead, and every player-driven removal goes through
deconstruct.

Worth removing rather than leaving inert -- it was a way to take a building out
of the world that skipped the refund and the queue, sitting in public view on the
class whose whole job is that lifecycle.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ne3mejABZoLWKLh8fgpM3x

src/lib/sim/BuildingSystem.cpp

@@ -403,27 +403,6 @@ BuildingId BuildingSystem::placeImmediate(FactoryState& state, BuildingType type
     return id;
 }
 
-bool BuildingSystem::removeBuilding(FactoryState& state, BuildingId id)
-{
-    for (std::vector<Building>::iterator it = state.buildings.begin();
-         it != state.buildings.end();
-         ++it)
-    {
-        if (it->id == id)
-        {
-            if (it->type == BuildingType::Belt || it->type == BuildingType::Splitter
-                || it->type == BuildingType::TunnelEntry || it->type == BuildingType::TunnelExit)
-            {
-                m_belts.removeTile(it->anchor);
-            }
-            state.grid.release(it->bodyCells);
-            state.buildings.erase(it);
-            return true;
-        }
-    }
-    return false;
-}
-
 void BuildingSystem::forEachBuilding(FactoryState& state, std::function<void(Building&)> fn)
 {
     for (Building& b : state.buildings)

src/lib/sim/BuildingSystem.h

@@ -112,10 +112,6 @@ public:
                             const std::vector<std::string>& surfaceMask,
                             QPoint anchor, Rotation rotation);
 
-    // Remove an operational building by id without refund (used for deaths).
-    // Returns true if found and removed.
-    bool removeBuilding(FactoryState& state, BuildingId id);
-
     // Mutable iteration over all operational buildings.
     void forEachBuilding(FactoryState& state, std::function<void(Building&)> fn);