Conda backend messing up access rights to base conda env on Windows

[Tolker-KU]

Describe the bug
When running a session the second time with conda as backend and not reusing the environment, the conda environment created by nox is deleted using shutil. Deleting a conda environment not using conda env remove results in conda going nuclear and messing up all sort of permissions on files on Windows. This includes files in the base conda environment.

I would suggest that a conda environment was deleted using conda env remove before deleting the directory when recreating environments. See https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html#removing-an-environment

How to reproduce
Running a simple session two times on Windows causes the problem.

@nox.session(venv_backend="conda")
def reproduce(session):
    session.conda_install("nox")

Expected behavior
The conda environment should be recreated without affecting anything else.