Hide underground subways from road map

Previously, the regular "road map" of a region would show not only
above-ground subway buildings (yellow "S"), but below-ground ones as
well, including all subway stations at underground labs (blue "S").

With the addition of the new "subway maintenance map", which reveals all
the underground subway lines, it makes sense to hide this information
from the regular road map (if it ever should have been shown at all).
This makes the subway map a more exclusive item, being the only map
showing underground subway stations.

data/json/items/book/maps.json

@@ -71,7 +71,7 @@
         "hospital",
         "school",
         "police",
-        "sub_station",
+        { "om_terrain": "sub_station", "om_terrain_match_type": "TYPE" },
         "bank"
       ],
       "message": "You add roads and points of interest to your map."