Make ansys-advanced/pyprojec.toml PEP 621 compliant

[jorgepiloto]

🐞 Problem

Similar situation as in #46. Duplicated instances of pyproject.toml for the build-system tools flit and poetry.

💡 Solution

Combine those into a single file.

[jorgepiloto]

Important: PEP 621 – Storing project metadata in pyproject.toml

In essence, previous pep tries to unify the way metadata is specified in the pyproject.toml file independently from the build-system being used.

However, it looks like poetry has not yet implemented this, see the following issues:

• https://github.com/python-poetry/poetry/issues/3332
• https://github.com/python-poetry/roadmap/issues/3