qmp: Clean up design of memchar-read The data returned has a well-defined size, which makes the size returned along with it redundant at best. Drop it. Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>