Documented the removal of the HMP command info cpustats

Signed-off-by: Bruno Larsen (billionai) <bruno.larsen@eldorado.org.br>
Message-Id: <20210531145629.21300-3-bruno.larsen@eldorado.org.br>
Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>
Reviewed-by: Lucas Mateus <lucas.araujo@eldorado.org.br>
Reviewed-by: Greg Kurz <groug@kaod.org>
[dwg: Fix a Sphinx formatting error]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>