Remove support for unlogged on partitioned tables

Remove support for unlogged on partitioned tables

The following commands were allowed on partitioned tables, with
different effects:
1) ALTER TABLE SET [UN]LOGGED did not issue an error, and did not update
pg_class.relpersistence.
2) CREATE UNLOGGED TABLE was working with pg_class.relpersistence marked
as initially defined, but partitions did not inherit the UNLOGGED
property, which was confusing.

This commit causes the commands mentioned above to fail for partitioned
tables, instead.

pg_dump is tweaked so as partitioned tables marked as UNLOGGED ignore
the option when dumped from older server versions.  pgbench needs a
tweak for --unlogged and --partitions=N to ignore the UNLOGGED option on
the partitioned tables created, its partitions still being unlogged.

Author: Michael Paquier
Reviewed-by: Nathan Bossart
Discussion: https://postgr.es/m/ZiiyGFTBNkqcMQi_@paquier.xyz