Reinstate Chesterton's fence now I get what it's doing

data/json/mapgen/map_extras/laststand.json

@@ -68,7 +68,6 @@
           [ "f_null", 150 ]
         ]
       },
-      "remove_vehicles": [ { "x": [ 0, 23 ], "y": [ 0, 23 ] } ],
       "place_monster": [ { "group": "GROUP_LAST_STAND", "x": [ 6, 17 ], "y": [ 6, 16 ], "chance": 100, "repeat": [ 10, 15 ] } ],
       "place_loot": [ { "group": "trash", "x": [ 6, 17 ], "y": [ 6, 16 ], "repeat": [ 5, 10 ] } ],
       "flags": [ "ERASE_ALL_BEFORE_PLACING_TERRAIN" ]

src/mapgen.cpp

@@ -5304,6 +5304,12 @@ static ret_val<void> apply_mapgen_in_phases(
     const jmapgen_objects &objects, const tripoint_rel_ms &offset, const std::string &context,
     bool verify = false )
 {
+    const ret_val<void> has_vehicle_collision = objects.has_vehicle_collision( md, offset );
+    if( verify &&  !has_vehicle_collision.success() ) {
+
+        return has_vehicle_collision;
+    }
+
     // We must apply all the mapgen in phases, but the mapgen is split between
     // setmap_points and objects.  So we have to make an outer loop over
     // phases, and apply each type restricted to each phase.