No functional changes intended.
The `insert_keyframe` function had a `bAction` argument that could be
a `nullptr`. If it was a `nullptr` it would be queried from the `ID`.
However in all cases where it is passed it is also gotten from the `ID`, making
the argument redundant.
This PR removes the argument to simplify the function.
Pull Request: https://projects.blender.org/blender/blender/pulls/119742
646f9bcebe