Remove semi-public C-API for doing arithmetic with Py_complex type

[h-vetinari]

@skirpichev

I’m not sure which issue link is canonical. Here is another one.

Funnily enough, I have comments on both of these^[1]

@skirpichev

Using a different compiler seems to be not a solution, as MSVC is a build requirement on Windows.

This topic came up recently: Introducing clang-cl as an alternative MSBuild backend

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1. I won’t comment on the UX of devcommunity. ↩︎