pgsql: Fix redundancy in error message

Fix redundancy in error message

Discussion: /messages/by-id/E1vEsbx-004QDO-0o@gemulon.postgresql.org

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/83122538f2f0354970cd5209a90abc677f32384e

Modified Files
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src/bin/pg_basebackup/pg_createsubscriber.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)