Evaluate additional core book removals for inclusion here.

I created this issue at the request of @quietone in https://www.drupal.org/project/drupal/issues/3376101#comment-15566005 📌 [11.x] [Meta] Tasks to remove Book Active

I think it was a follow up in case the other issues needed to be updated here, the others are all closed so I think we can evaluate.

📌 Remove Book usage from Umami Fixed - likely no change needed here.
📌 Update comments to not reference Book since it has been removed Fixed - likely no change needed here.
📌 Update cspell.json to remove references to extensions no longer in core Fixed - I don't see a cspell override in this module which I *think* means it uses core's settings, now that core has removed the fixtures from cspell you will need to probably ignore them in a custom cspell ignore rule here.

Did this mean to be in book contrib?

I think you can close this, quietone wanted me to open this in case there needed to be a backport. I don't see anything that needs that.