Make more use of makeColumnDef()
Since we already have it, we might as well make full use of it,
instead of assembling ColumnDef by hand in several places.
Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://www.postgresql.org/message-id/flat/
52a125e4-ff9a-95f5-9f61-
b87cf447e4da@eisentraut.org