Remove unused returned value.
Remove unused returned value.

In previous implementations, the attributes had the units removed, but with the current this doesn't happen and the returned value is exactly the same as the input.

openforcefield/openff-toolkit,openforcefield/openff-toolkit,open-forcefield-group/openforcefield,open-forcefield-group/openforcefield,open-forcefield-group/openforcefield