When keyframing with the `Only Insert Needed` flag enabled,
the code was able to delete keyframes in certain cases.
This behavior is removed and replaced with the following rules.
* If there is a key on the current frame, and it has the same value, skip it.
* If there is no key, but the FCurve evaluates to the same value, skip it.
* Add a key in all other cases.
Remove that functionality for consistency and simplify the code around it.
Pull Request: https://projects.blender.org/blender/blender/pulls/115360
83287624bc