textproc/py-mdformat: Update to 1.0.0

• Remove files/patch-pyproject.toml
• Fix pyproject.toml (via a post-patch target), because the build framework does not recognise its new format. (see https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files )
• Pet port(clippy|fmt)

ChangeLog: https://mdformat.readthedocs.io/en/stable/users/changelog.html#id1