pgsql: doc: Update pg_upgrade documentation to match recent description

doc: Update pg_upgrade documentation to match recent description changes.

Commit 792353f7d52 updated the pg_dump and pg_dumpall documentation to
clarify which statistics are not included in their output. The pg_upgrade
documentation contained a nearly identical description, but it was not updated
at the same time.

This commit updates the pg_upgrade documentation to match those changes.

Backpatch to v18, where commit 792353f7d52 was backpatched to.

Author: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Reviewed-by: Bruce Momjian <bruce(at)momjian(dot)us>
Discussion: https://postgr.es/m/CAHGQGwFnfgdGz8aGWVzgFCFwoWQU7KnFFjmxinf4RkQAkzmR+w@mail.gmail.com
Backpatch-through: 18

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d984cef87c66094452be26859796f4b820f8d655

Modified Files
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doc/src/sgml/ref/pgupgrade.sgml | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)