release-notes 19.09: removal of non-LTS kernel attrs

Even though the release obviously already happened, I think it might
still make sense to add a short note about the attributes not being
supported any longer (and going forward).

(cherry picked from commit 7163d3a9df35904d0c9acc9f643fd70ee3108539)
(cherry picked from commit a64b8c3c191af1317cfdc1ea4f4e5f881c4cf503)