remove special handling of rail

Skip railway=rail in the style, so that installations can remove
it if they wish.

settings/import-extratags.style

@@ -98,6 +98,7 @@
     "values" : {
         "level_crossing" : "skip",
         "no" : "skip",
+        "rail" : "extra",
         "" : "main,with_name"
     }
 },

settings/import-full.style

@@ -98,6 +98,7 @@
     "values" : {
         "level_crossing" : "skip",
         "no" : "skip",
+        "rail" : "skip",
         "" : "main,with_name"
     }
 },

sql/functions/placex_triggers.sql

@@ -62,8 +62,6 @@ BEGIN
     ELSEIF NEW.class = 'boundary' AND NEW.type = 'administrative'
            AND NEW.admin_level <= 4 AND NEW.osm_type = 'W' THEN
         return NULL;
-    ELSEIF NEW.class = 'railway' AND NEW.type in ('rail') THEN
-        return NULL;
     ELSEIF NEW.osm_type = 'N' AND NEW.class = 'highway' THEN
         NEW.rank_search = 30;
         NEW.rank_address = 0;