Remove nox file

[kasium]

We'll use github actions with a test matrix instead. This allows parallel test runs with different python/sqlalchemy versions as in nox

[jarus]

What about local development activities where you want to test upfront multiple python versions and sqlalchemy versions?

[kasium]

Valid point but I hope that this will be a corner case. Also using nox in parallel way is painful and using github-actions matrix is easier. Maintaining both will be too complicated