I do not want to keep the animation node trees in the blender file, however, even when I remove the fake user from them, save, and restart the file, the animation node trees are still there. They won't go away no matter what I've tried.
- Open the node tree in the node editor.
- While hovering over the node editor press space bar.
- Search for Remove Animation Node Tree.
- Execute the operation.
This should remove the tree completely.
I know it is a bit weird that you can't just delete the tree like others, the reason for it is a bit more technical. I don't want to go into details now.
The next version of AN will have a button in the footer/header of the node tree to remove the tree.