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/transportation_name/update_route_member.sql

@@ -56,7 +56,6 @@ BEGIN
           THEN 'ca-transcanada'::route_network_type
         WHEN network = 'omt-gb-motorway' THEN 'gb-motorway'::route_network_type
         WHEN network = 'omt-gb-trunk' THEN 'gb-trunk'::route_network_type
-        ELSE NULL
       END
   ;