Remove commented and legacy code in floris_interface.py (#397)

* Remove remnants of uncertainty modeling in floris_interface

* Remove get_turbine_power and farm power legacy functions that are already commented out

* Remove additional commented code

Co-authored-by: Rafael M Mudafort <rafael.mudafort@nrel.gov>
Co-authored-by: Rafael M Mudafort <rafmudaf@gmail.com>