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/place/capital.sql

@@ -3,6 +3,5 @@ RETURNS INT AS $$
     SELECT CASE
         WHEN capital IN ('yes', '2') THEN 2
         WHEN capital = '4' THEN 4
-        ELSE NULL
     END;
 $$ LANGUAGE SQL IMMUTABLE STRICT;