doc: Remove reference to recovery params for divergence lookup in pg_rewind

The documentation of pg_rewind mentioned the use of restore_command and
primary_conninfo as options available at startup to fetch missing WAL
segments that could be used to find the point of divergence for the
rewind.  This is confusing because when finding the point of divergence
the target cluster is offline, so this option is not available.

Issue introduced by 878bd9a, so backpatch down to 9.6.  The
documentation of 13 and HEAD was already right as this sentence has been
changed by a7e8ece when introducing -c/--restore-target-wal.

Reported-by: Amine Tengilimoglu
Discussion: https://postgr.es/m/CADTdw-w_0MP=iQrfizeU4QU5fcZb+w8P_oPeLL+WznWf0kbn3w@mail.gmail.com
Backpatch-through: 9.6

Author: michaelpq

doc/src/sgml/ref/pg_rewind.sgml

@@ -68,12 +68,10 @@ PostgreSQL documentation
    shut down soon after the divergence, this is not a problem, but if the
    target cluster ran for a long time after the divergence, the old WAL
    files might no longer be present. In that case, they can be manually
-   copied from the WAL archive to the <filename>pg_wal</filename> directory, or
-   fetched on startup by configuring <xref linkend="guc-primary-conninfo"/> or
-   <xref linkend="guc-restore-command"/>.  The use of
-   <application>pg_rewind</application> is not limited to failover, e.g.,  a standby
-   server can be promoted, run some write transactions, and then rewound
-   to become a standby again.
+   copied from the WAL archive to the <filename>pg_wal</filename> directory.
+   The use of <application>pg_rewind</application> is not limited to
+   failover, e.g., a standby server can be promoted, run some write
+   transactions, and then rewound to become a standby again.
   </para>
 
   <para>