doc: Fix outdated doc in pg_rewind.

Update pg_rewind documentation to reflect the change that data checksums are
now enabled by default during initdb.

Backpatch to v18, where data checksums were changed to be enabled by default.

Author: Zhijie Hou <houzj.fnst@fujitsu.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/TY4PR01MB16907D62F3A0A377B30FDBEA794B2A@TY4PR01MB16907.jpnprd01.prod.outlook.com
Backpatch-through: 18

doc/src/sgml/ref/pg_rewind.sgml

@@ -117,9 +117,9 @@ PostgreSQL documentation
    <application>pg_rewind</application> requires that the target server either has
    the <xref linkend="guc-wal-log-hints"/> option enabled
    in <filename>postgresql.conf</filename> or data checksums enabled when
-   the cluster was initialized with <application>initdb</application>.  Neither of these
-   are currently on by default.  <xref linkend="guc-full-page-writes"/>
-   must also be set to <literal>on</literal>, but is enabled by default.
+   the cluster was initialized with <application>initdb</application> (the
+   default).  <xref linkend="guc-full-page-writes"/> must also be set to
+   <literal>on</literal>, but is enabled by default.
   </para>
 
   <warning>