Drop support to unsupported python and django versions

[jairhenrique]

https://endoflife.date/python
https://endoflife.date/django

[vitalik]

I would keep for now python3.7 (I still see 1.5% of downloads using it) and it is supported by pydantic

and django ~3.1 is still used in the wild (as I know from some feedbacks)

So i would rather keep deps as it is - to give people less headaches migrating to ninja-v1

on the other hand django 2.x and 3.0 can be dropped (but then need to cleanup ninja.compatibility package)

[jairhenrique]

@vitalik done!

[vitalik]

Thank you