doc:process: remove note from 'stable api nonsense'

The link referred by the note can't be retrieved: this patch just
remove that old note.

Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>