pg_dump: fix mis-dumping of non-global default privileges.

pg_dump: fix mis-dumping of non-global default privileges.

Non-global default privilege entries should be dumped as-is,
not made relative to the default ACL for their object type.
This would typically only matter if one had revoked some
on-by-default privileges in a global entry, and then wanted
to grant them again in a non-global entry.

Per report from Boris Korzun.  This is an old bug, so back-patch
to all supported branches.

Neil Chen, test case by Masahiko Sawada

Discussion: https://postgr.es/m/111621616618184@mail.yandex.ru
Discussion: https://postgr.es/m/CAA3qoJnr2+1dVJObNtfec=qW4Z0nz=A9+r5bZKoTSy5RDjskMw@mail.gmail.com