remove module from singlediode function arguments

[wholmgren]

I'm just now realizing that the module argument to our singlediode function is nearly pointless. module['V_oc_ref'] is used to set the initial guess for the p_mp numerical solution, and I'm pretty sure that it can be replaced with the calculated v_oc. This will simplify the api and bring us back into consistency with the matlab library.

[cwhanse]

I agree