installer: simplify logic for calculating operations regarding extras and fix small bug (#9345)

* Operations are completely calculated in `Transaction.calculate_operations()` so that we do not have to remember extra uninstalls between two calculations.
* Previously, extras that were not requested were not uninstalled when running `poetry install` (without extras) if there was no lockfile, now it does not matter if there was a lockfile or not.
* In `installer._get_extra_packages()` we do not have to distinguish between locked extras and extras in the pyproject.toml because both must be consistent.