man: remove note about shutdown being legacy

This can only confuse people, because there's no need to
discourage people from using shutdown. It is fully functional
and supported.

man/shutdown.xml

@@ -168,13 +168,6 @@
                 code otherwise.</para>
         </refsect1>
 
-        <refsect1>
-                <title>Notes</title>
-
-                <para>This is a legacy command available for
-                compatibility only.</para>
-        </refsect1>
-
         <refsect1>
                 <title>See Also</title>
                 <para>