Remove dependency on SymPy.jl

[ufechner7]

For me SymPy.jl fails to compile on 2 of 3 PCs. Second best option would be https://github.com/jverzani/SymPyPythonCall.jl/, best option not being dependent on Python.

[baggepinnen]

SymPy is a fundamental core dependency of this package and this will not be changed

[ufechner7]

First question: Which feature does SymPy.jl provide that SymPyPythonCall.jl doesn't provide?

Second question: Which features are missing in Symbolics.jl for implementing the conversion of a symbolic s expression into a transfer function?

[baggepinnen]

Which feature does SymPy.jl provide that SymPyPythonCall.jl doesn't provide?

I don't know, and since this package is working perfectly fine on my machine and on the CI runner, I cannot motivate spending time figuring it out.

Which features are missing in Symbolics.jl for implementing the conversion of a symbolic s expression into a transfer function?

I don't know, Symbolics is missing a lot of features, like documentation, stability and maturity.

[ufechner7]

https://github.com/JuliaPy/PythonCall.jl is the future...

[ufechner7]

I cannot motivate spending time figuring it out.

The question is, would you accept a pull request that replaces PyCall with PythonCall?

[baggepinnen]

I have nothing against switching, I just cannot motivate spending time on it. If you submit a PR that makes the change (and that change alone), that'd be fine by me