This PR removes a check that always tried to autocomplete a class using its __init__ function.

In fact, the inspect module (used afterwards in

) does a much better job at finding the arguments that are actually typing a class, which aren't always the ones in __init__. Since at least Python 3.6, it handles __call__, __new__ and __signature__ in addition to __init__, so restricting the signatures to __init__ is actually a downgrade.
See https://github.com/python/cpython/blob/2c56c97f015a7ea81719615ddcf3c745fba5b4f3/Lib/inspect.py#L2284

I'm raising this issue because our CLI requires __signature__ to work, which is the case if you let inspect.signature do its job by default but not if you manually select cls.__init__ 🙂

Note: I also doubt that the __new__ check below is useful on modern Python versions, since __new__ is also checked by inspect.signature (therefore by inspection.getfuncprops), but I didn't remove it in this PR.