Editable children property persists after node deletion

[KoBeWi]

Godot version:
3.1.1

Issue description:
Editable children property is stored as NodePaths in scene root and they aren't removed/updated on node move/update, which leads to unexpected results (like #20409).

Steps to reproduce:

1. Create a scene (e.g. SceneA.tscn)
2. Create another scene (e.g. SceneB)
3. Create a main scene
4. Instance SceneA
5. Toggle editable children of SceneA
6. Delete SceneA
7. Instance SceneB
8. Rename SceneB to SceneA
9. SceneB will get editable children upon rename

Minimal reproduction project:
ReproductionProject.zip
Initial setup for point 3 in steps to reproduce.

[KoBeWi]

Still valid in 241e709 like other similar issues.