Clarify remove_stale_contenttypes data loss warning

[Johannes Maron]

I just wanted to remove stale contenttypes from a system and noticed a pretty significant bug.

The command prints a message before you need to confirm the deletion that reads:

This list doesn't include any cascade deletions to data outside of Django's models (uncommon).

However, a quick investigation on the objects that are to be deleted includes objects outside of Django's scope.
In my case:

• 2 auth.Group_permissions object(s)
• 7185 joeflow.Task object(s)
• 5519 joeflow.Task_parent_task_set object(s)

This misinformation can cause users to delete data without double-checking.

[Tim Graham]

I think you've misunderstood the message. The data you listed seem to be Django objects and relations. Why do you say they are "outside of Django's scope"? Aren't they printed as part of the deletion warning?

[Johannes Maron]

Oooooh, now I get it. Wow, OK, is it just me, or is that sentence misleading? Maybe we replace that sentence something that doesn't include brackets at the end and not the term "Django's models"? Something a long the lines of:

The list above does not include deletions that may be caused by manually added database constraints or triggers.

[Tim Graham]

I wrote the original sentence in e2dfa81ff7489d97700604d634adacf1384af184. I guess you may have interpreted "Django's models" to mean contrib.auth? I don't have an objection to some rewording but for me, it's more intuitive to talk about "cascade deletions" and "relations" rather than "constraints or triggers." Feel free to submit a PR to continue the discussion with a merger.