pgsql: doc: Update pg_dump/dumpall/upgrade about handling of external s

doc: Update pg_dump/dumpall/upgrade about handling of external statistics

The pages of pg_dump, pg_dumpall and pg_upgrade mentioned that their
--no-statistics and --statistics options did not include the handling of
statistics created by CREATE STATISTICS, which was wrong.

Oversight in c32fb29e979d.

Reported-by: Igi Izumi <igi@sraoss.co.jp>
Discussion: /messages/by-id/19529-c7eb1e7a0b07eae6@postgresql.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f0a4f280b4d3cd16c368c524fe0c212643615f46

Modified Files
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doc/src/sgml/ref/pg_dump.sgml | 1 -
doc/src/sgml/ref/pg_dumpall.sgml | 1 -
doc/src/sgml/ref/pgupgrade.sgml | 3 +--
3 files changed, 1 insertion(+), 4 deletions(-)