Remove nonfunctional geometry engines
Remove nonfunctional geometry engines

There were two geometry engines that had some issues:

1. OmegaFFGeometryEngine: this geometry engine performed rather poorly,
as it fails to appropriately take into account the positions of previous atoms when
placing new atoms. Also, it did not have an implementation of the
logp_reverse and as such was not useful.

2. SplineTorsionGeometryEngine: this geometry engine occasionally had
negative probabilities because of spline artifacts.

choderalab/perses,choderalab/perses