Remove ancient special case code for dropping oid columns
The special handling of negative attribute numbers in
RemoveAttributeById() was introduced to support SET WITHOUT OIDS
(commit
24614a9880). But that feature doesn't exist anymore, so we
can revert to the previous, simpler version.
Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://www.postgresql.org/message-id/flat/
52a125e4-ff9a-95f5-9f61-
b87cf447e4da@eisentraut.org