pycompat: remove large Python 2 block
We no longer support Python 2. So we can delete its compatibility
code and remove the conditional and dedent the Python 3 code.
In order to make the linter happy, we had to inline imports in the
stanza at the top of the file.
Differential Revision: https://phab.mercurial-scm.org/D12250
[build-system]
requires = ["setuptools", "wheel"]
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true