delete the unused getAllBeltTiles and BeltTileInfo

Nothing in lib, ui, balancing or the tests calls it — the only references were
its own declaration and definition.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YHcUerKAZKWNvSKJxYKbnG

src/lib/sim/BuildingSystem.h

@@ -119,14 +119,6 @@ public:
     void tickOutputBelts();
 
     // -- Queries -------------------------------------------------------------
-    struct BeltTileInfo
-    {
-        BuildingId     buildingId;
-        QPoint       tile;
-        BuildingType type;       // Belt or Splitter
-        Rotation     directionA; // Belt: its direction; Splitter: first output
-        Rotation     directionB; // Splitter: second output; Belt: same as directionA
-    };
 
 
     // REQ-UI-DEBUG-OVERLAY "Max Factory Production": count of completed
@@ -139,7 +131,6 @@ public:
     // nullopt for building types that show no light (belts, splitters, tunnels,
     // HQ, defence stations). The Salvage Bay is a two-state special case:
     // Producing while its output buffer holds scrap, Starved when empty.
-    std::vector<BeltTileInfo> getAllBeltTiles()             const;
 
     // Visits every item currently emerging from a building output port on its
     // virtual output belt (REQ-MAT-OUTPUT-EMERGE), passing the item type and its