Remove setuptools dependency

[aeisenbarth]

I could be mistaken, but to me it seems python-readchar should not specify setuptools as install requirement. Typically it is provided by the environment, or specified as build requirement. It is never imported and used in order to run readchar.

As a consequence, a specific version of setuptools leaks into my lock files and I have to specifically exclude it.

See also #111. In pyproject.toml, there would be:

[build-system]
requires = ["setuptools", "wheel"]

[project]
dependencies = [
]

[aeisenbarth]

Similar case Gandi/gandi.cli#249
See also: https://stackoverflow.com/questions/65326080/python-setup-config-install-requires-good-practices

[aeisenbarth]

Thanks!