pgsql: Fix redundancy in error message

Fix redundancy in error message

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

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/150e24501bc218057a7b9a24b19a145fa8b5c678

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