Cleanup: Remove TileMatrix that hasn't been used for 4+ years. (#12621)

This 'nice' structure was left around from #8258 just in case it might be used again.

Spoiler alert: it hasn't.

This removes manual memory management. And otherwise unused and untested code.

src/saveload/town_sl.cpp

@@ -18,12 +18,9 @@
 #include "../landscape.h"
 #include "../subsidy_func.h"
 #include "../strings_func.h"
-#include "../tilematrix_type.hpp"
 
 #include "../safeguards.h"
 
-typedef TileMatrix<CargoTypes, 4> AcceptanceMatrix;
-
 /**
  * Rebuild all the cached variables of towns.
  */
@@ -182,6 +179,12 @@ public:
 };
 
 class SlTownAcceptanceMatrix : public DefaultSaveLoadHandler<SlTownAcceptanceMatrix, Town> {
+private:
+	/** Compatibility struct with just enough of TileMatrix to facilitate loading. */
+	struct AcceptanceMatrix {
+		TileArea area;
+		static const uint GRID = 4;
+	};
 public:
 	inline static const SaveLoad description[] = {
 		SLE_VAR(AcceptanceMatrix, area.tile, SLE_UINT32),