Remove weird DUKW spawns (#74467)

* Remove weird DUKW spawns

These are vanishingly rare, there is potential to have literally one or two spawning in the whole game as they are sometimes operated as tour vehicles, but having them spawn randomly in marinas or out in the water at any rate is nonsense.

* json styling

data/json/vehicle_groups.json

@@ -129,14 +129,7 @@
   {
     "type": "vehicle_group",
     "id": "boatrent",
-    "vehicles": [
-      [ "canoe", 2000 ],
-      [ "kayak", 1500 ],
-      [ "kayak_racing", 500 ],
-      [ "DUKW", 250 ],
-      [ "raft", 2000 ],
-      [ "wood_rowboat_double", 1500 ]
-    ]
+    "vehicles": [ [ "canoe", 2000 ], [ "kayak", 1500 ], [ "kayak_racing", 500 ], [ "raft", 2000 ], [ "wood_rowboat_double", 1500 ] ]
   },
   {
     "type": "vehicle_group",
@@ -146,7 +139,7 @@
   {
     "type": "vehicle_group",
     "id": "lake",
-    "vehicles": [ [ "DUKW", 250 ], [ "cabin_cruiser_wood", 1500 ] ]
+    "vehicles": [ [ "cabin_cruiser_wood", 1500 ] ]
   },
   {
     "type": "vehicle_group",