Remove `molecule` from `IntegralHelper`

[gustavojra]

It is pointless since a BasisSet is mandatory and it contains molecule already. Moreover, it can be a source of bugs. Currently (v0.3.0). Fermi will ignore molecule inputs given directly to the IntegralHelper. I have that fixed, needs PR.

[SeptemberMy]

Hi, @gustavojra, I guess this modification caused the failure of the code Vnuc = aoints.molecule.Vnuc in examples/MyRHF.ipynb.

[gustavojra]

I will check on it! That should be an easy fix.