Duplicate Notes header in PVSystem.fuentes_celltemp method

Duplicate Notes heading [here](https://github.com/pvlib/pvlib-python/blob/c17f7281c168caa7b68a2901b7e6116670138be6/pvlib/pvsystem.py#L724).  The second Note doesn't appear in the method [documentation](https://pvlib-python.readthedocs.io/en/stable/generated/pvlib.pvsystem.PVSystem.fuentes_celltemp.html)