basecamps: Deprecate initial construction of the primitive camp

The modular field camp does everything that the primitive field camp
does, but is a better design.  Remove the "Old Camp" from the list
of available camps.  Existing camps will not be affected, but people
will not be able to start new camps using the Old Camp mapgen.

data/json/recipes/basecamps/recipe_groups.json

@@ -5,7 +5,6 @@
     "building_type": "NONE",
     "recipes": [
       { "id": "faction_base_modular_hub_field_0", "description": "Field Camp", "om_terrains": [ "field" ] },
-      { "id": "faction_base_camp_0", "description": "Old Camp", "om_terrains": [ "field" ] },
       { "id": "faction_base_firestation_0", "description": "Firestation Base", "om_terrains": [ "fire_station" ] }
     ]
   },