remove from API reference docs

Author: kandersolar

docs/sphinx/source/reference/effects_on_pv_system_output/spectrum.rst

@@ -8,7 +8,6 @@ Spectrum
 
    spectrum.spectrl2
    spectrum.get_example_spectral_response
-   spectrum.get_am15g
    spectrum.get_reference_spectra
    spectrum.calc_spectral_mismatch_field
    spectrum.spectral_factor_caballero