Remove tomlkit regression mitigation

In #5673 we introduced a mitigation for a `tomlkit` regression on Windows. The root cause of this has to be identified, addressed and mitigation addressed.

Mitigation commit: https://github.com/python-poetry/poetry/commit/1d71955b7a0e5c3cbe90a5d30a680af22e575e26