pgsql: doc: Clarify pg_combinebackup's --sync-method description

doc: Clarify pg_combinebackup's --sync-method description

The --sync-method documentation, copied from pg_basebackup,
referred to "the plain format", although pg_combinebackup always
produces a plain data directory. It also called the directory being
synchronized the "backup directory", which could be confused with an
input backup directory.

Remove the inapplicable format qualifications and explicitly
identify the output directory as the synchronization target.

Backpatch to v17, where pg_combinebackup was introduced.

Author: Sai Pranav <rajasaipranav0(at)gmail(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAPHduZAYBNVWkXAsrXXrb+dD2gKDABcJfcudXQecFdW2WEpDdw@mail.gmail.com
Backpatch-through: 17

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/25cf49592c6ee8e45c75899e4faa7b9088b54611

Modified Files
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doc/src/sgml/ref/pg_combinebackup.sgml | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)