Remove the legacy (aka backward-compatible) API from `bpy.types.Action`:
- `action.fcurves`
- `action.groups`
- `action.id_root`
These have been deprecated since the introduction of Slotted Actions in
Blender 4.4. They operated on a subset of the Action's data, which was
not guaranteed to be the correct subset, given the Action's new
possibilities. This was to give add-on developers time to migrate to the
new API, and has always been intended to be removed in Blender 5.0.
See #146586 for more info.
Pull Request: https://projects.blender.org/blender/blender/pulls/146626
1395abc502