Cleanup unused code

Remove unused, undocumented functions in ase.utils.ff.

I'd like to remove some more untested functions but they're used by ase.opt.precon. Can we remove them, @jameskermode, or might there be a unittest?

Unfortunately this module has a lot of duplicated code. It would be best to use functions and classes to avoid such duplication.

I'll take the liberty of merging since the functions here are clearly no longer in use. Please let me know about remaining untested functions in ase.utils.ff though, @jameskermode, or if there's more to this than meets the eye. You can see which functions are untested here: http://ase.gitlab.io/ase/_builds_ase_ase_ase_utils_ff_py.html

mentioned in commit d4578033

merged

Oops, I completely missed this. Will try to take a look at the remaining unused functions ASAP- the original author of this part of the code, has now left academia so I agree that consolidating on a well-tested subset is important.

Thank you. Feel free to open an issue for discussing.