now that layout-test-results are automatically being attached to bugs, i suggest that a cron job or other maintenance mechanism should delete obsoleted layout-test-results attachments; to do this, it would be useful to add a keyword DeleteObsoleteLayoutResults when the first layout-test-results are added, and then, on a regular basis, delete layout-test-results attachments whose bug is marked with this keyword and which attachments have been marked as obsolete if the dev doesn't want them deleted after obsoleting, then they can remove the keyword to prevent automatic deletion