Comment 2 for bug 1334576

When I look at a fresh installation, there is a cron job registered for cron_clean_internal_activity_notifications, that calls PluginNotificationInternal::clean_notifications, but the delay is set to 182 days and not 60, and the only notification types, that are actually deleted, are viewaccess, watchlist and institutionmessage.
I'm not sure about deleting whatever notification after a fixed time, when a user isn't able to store away messages he does not want deleted. Though viewaccess and watchlistnotification probably won't hurt.