remove postcodes entirely from indexing

place=postcode places are artificial places that collect addr:postcode
points for aggration. They should neither show up in the address nor
be searchable. That means that there is no need to index them at all.
Only let boundary=postal_code through which define correct areas for
postcodes.

sql/functions/ranking.sql

@@ -145,10 +145,6 @@ BEGIN
   THEN
     SELECT * INTO search_rank, address_rank
       FROM get_postcode_rank(country, postcode);
-
-    IF NOT extended_type = 'A' THEN
-      address_rank := 0;
-    END IF;
   ELSEIF extended_type = 'N' AND place_class = 'highway' THEN
     search_rank = 30;
     address_rank = 0;