pgsql: Fix documentation comment for pg_md5_hash

Fix documentation comment for pg_md5_hash

Commit b69aba74578 added the errstr parameter to pg_md5_hash but
missed updating the synopsis in the documentation comment. The
follow-up commit 587de223f03 added the parameter to the list of
outputs. The returnvalue had been changed from integer to bool
before that but remained in the synopsis. This fixes both.

Author: Tatsuro Yamada <tatsuro.yamada@ntt.com>
Discussion: /messages/by-id/TYYPR01MB82313576150CC86084A122CD9E292@TYYPR01MB8231.jpnprd01.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6b41ef03306f50602f68593d562cd73d5e39a9b9

Modified Files
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src/common/md5_common.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)