Commit 16f72448 added this parameter
to the documentation, including a note that it is deprecated. But it
has never been added to the "Deprecated features" appendix, which is
our official way to deprecate legacy parameters. So let's do this now.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>