Move heal locations data to their associated map.json (#2034)

data/maps/SouthernIsland_Exterior/map.json

@@ -67,5 +67,12 @@
       "player_facing_dir": "BG_EVENT_PLAYER_FACING_ANY",
       "script": "SouthernIsland_Exterior_EventScript_Sign"
     }
+  ],
+  "heal_locations": [
+    {
+      "id": "HEAL_LOCATION_SOUTHERN_ISLAND_EXTERIOR",
+      "x": 15,
+      "y": 20
+    }
   ]
 }