Since partitioned tables in pg12 do not have toast tables, trying to set
the toast OID confuses pg_upgrade.  Have pg_dump omit those values to
avoid the problem.

Per Andres Freund and buildfarm members crake and snapper
Discussion: https://postgr.es/m/20190306204104.yle5jfbnqkcwykni@alap3.anarazel.de