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_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/726e77d7a94fd6d6ad99e439351ae6d4a48d3441

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