pg_rewind: Remove notice in docs about running CHECKPOINT after promote.

Commit 009eeee made it unnecessary. pg_rewind now works on a
recently promoted standby.

Author: Kyotaro Horiguchi, Keisuke Kuroda
Discussion: https://www.postgresql.org/message-id/aeb5f31a-8de2-40a8-64af-ab659a309d6b%40iki.fi

Author: hlinnaka

doc/src/sgml/ref/pg_rewind.sgml

@@ -335,15 +335,6 @@ GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text, bigint, bigint, b
 </programlisting>
   </para>
 
-  <para>
-   When executing <application>pg_rewind</application> using an online
-   cluster as source which has been recently promoted, it is necessary
-   to execute a <command>CHECKPOINT</command> after promotion such that its
-   control file reflects up-to-date timeline information, which is used by
-   <application>pg_rewind</application> to check if the target cluster
-   can be rewound using the designated source cluster.
-  </para>
-
   <refsect2>
    <title>How It Works</title>