None return type shown even if explicitly hidden on overloaded calls

[laurensvalk]

Throughout the docs, we do not show ---> None to keep things easy to follow. See #99 for rationale.

But on overloaded cases, Sphinx makes them show up on all but the first one.

    """
    qstr_info()
    qstr_info(verbose)                       # <---- There's nothing here but still it shows up

    Prints how many strings are interned and how much RAM they use.

[laurensvalk]

This is a styling issue and we don't have many occurrences of this one, so let's not block V3.2 on it.