Leftover `sys.path` in `bose_einstein_condensate_3D_comoving_frame.ipynb`

[flokno]

I think this PATH import should be removed:

https://github.com/vidarsko/ComFiT/blob/main/tutorial/bose_einstein_condensate_3D_comoving_frame.ipynb?short_path=031aa90#L145

[vidarsko]

Thanks! Removed.