get rid of future dependency

[blshkv]

https://github.com/dirkjanm/BloodHound.py/blob/master/setup.py#L16

The "future" project is dead, the latest release was back in 2019-10-30, see https://python-future.org/
It is also vulnerable to CVE-2022-40899, may be others.

Please migrate to python3 and forget about python2.

[dirkjanm]

Good point, we already dropped py2 support a while ago in this project so the dependency on future isn't needed anymore. I'll make sure to remove code references to it