Remove unneeded "else null" in conditions (#732)

Minor code cleanup:
SQL already returns NULL in the "WHEN" condition
if it is not matched by any of the cases.

Co-authored-by: Eva Jelinkova <evka.jelinkova@gmail.com>

layers/poi/update_poi_point.sql

@@ -27,7 +27,6 @@ BEGIN
   SET agg_stop = CASE
       WHEN p.subclass IN ('bus_stop', 'bus_station', 'tram_stop', 'subway')
         THEN 1
-      ELSE NULL
   END;
 
   UPDATE osm_poi_point p
@@ -36,7 +35,6 @@ BEGIN
         WHEN p.subclass IN ('bus_stop', 'bus_station', 'tram_stop', 'subway')
             AND r.rk IS NULL OR r.rk = 1
           THEN 1
-        ELSE NULL
       END)
     FROM osm_poi_stop_rank r
     WHERE p.osm_id = r.osm_id