Remove stream kwarg of read_env()

[hukkin]

Remove the stream kwarg of read_env().

Firstly, the kwarg is incorrectly type annotated. It is annotated as str and is passed as a kwarg to dotenv.load_dotenv(). That kwarg of dotenv.load_dotenv(), however, takes an io.StringIO, not a string.

Secondly, I believe the stream kwarg never does anything here. dotenv.load_dotenv() only uses the stream kwarg if its first kwarg (dotenv_path) is falsy. It seems to me that we always pass a truthy value to that, so stream is never used. Therefore I suggest we remove it.

I recommend running mypy with access to site-packages and their typehints in CI (mypy in pre-commit runs in a venv with no site-packages, unless dependencies listed in .pre-commit-config.yaml). It would catch this and a few other issues.

[sloria]

Good catch!

As for running mypy on dependencies, feel free to send a PR for that; I won't have time to look into it in the short term.