Cleaning up TNEP line on/off constraints about powermodels.jl

[rb004f]

From a mathematical perspective, these constraints are identical (different on/off variables). So, should be possible.

[ccoffrin]

I see the issue. The functions used in constraint_complex_voltage_on_off, implicitly call the standard versions of the variables, while constraint_complex_voltage_ne needs the "_ne" versions. Will think about how to unify these.

[rb004f]

And we can't directly use the "standard" versions of the variables, because that would preclude us from creating a model with both line switching and expansion planning.