remove badelf's copy of acf 🧝

[jacksund]

• closes badelf and bader ACF classes need merged #561

there were only 2 differences between our files:

1. how we filter off warnings
2. how we set the empty atom. In yours, you assume He (what I used to do). In mine, I determine the missing element and determine that it is the empty

[jacksund]

@SWeav02 this PR is ready for review

[SWeav02]

This looks fine to me. The only other thing I remember changing was the line chgcar_empty_filename = directory / "CHGCAR_empty" to chgcar_empty_filename = directory / "CHGCAR_electride". I think we ought to change the nomenclature for all of the instances of GHCAR_empty or ELFCAR_empty because to me it implies some sort of empty structure or file. I'll open an issue about this.

[jacksund]

sounds good. There might be a better option that fits both cases. You're right about _empty being misleading + I avoided _electride bc that might not catch all use-cases with empty atoms. Maybe _w_empty_atoms -- make it verbose and clear?