Cleaned up constructor and destructor for Potential_Paris_3D.
Cleaned up constructor and destructor for Potential_Paris_3D.

evaneschneider/cholla,evaneschneider/cholla,cholla-hydro/cholla,cholla-hydro/cholla,cholla-hydro/cholla,evaneschneider/cholla,evaneschneider/cholla,cholla-hydro/cholla