Perf optimization: use EXCEPT instead of NOT IN
Perf optimization: use EXCEPT instead of NOT IN

With javitonino's help, greatly reduce the processing time by using
EXCEPT instead of NOT IN, which causes it to use a `HashSetOp Except`
plan on the subqueries rather than a `Seq Scan` on `Materialize`'d
subtables.

CartoDB/cartodb-postgresql,CartoDB/cartodb-postgresql