Attempt to generate .uis deps free lock file

Since `poetry` doesn't seem to actually mark optional group deps as such
in the lock file (!?) manually generate a `poetry.lock` with the
optional groups commented out in the `pyproject.toml`; this is all in
an attempt at trying to make `poetry2nix` build without any UI components
which seem to be the source of much frustration without hacking on p2n
and/or nixpkgs repos..

Further drop all the old build system files including the
setup.py and requirements.txt files.