Remove use and definitions of serialize_numpy and deserialize_numpy from gufe.molhashing

[ianmkenney]

The serialize_numpy and deserialize_numpy functions are only used in ProteinComponent and SmallMoleculeComponent _to_dict and _from_dict methods. Since we have custom JSON codecs that handle numpy arrays, these functions don't appear to be necessary and might make handling these classes in dict-form cumbersome.