Deprecate all LegacyDriver related code

[mrossinek]

What is the expected enhancement?

The legacy driver results, QMolecule and WatsonHamiltonian, have been deprecated in Qiskit Nature 0.2.0.
We currently still have various places where we use them via their public API in order to provide migration/conversion utilities. Most notably in the HDF5Driver (as pointed out here) and in the property framework via the .from_legacy_driver_result conversion methods.

In order to be able to actually remove these legacy driver results, we must first deprecate all methods which use them in their public API. Ideally, we add these deprecations as part of 0.4.0
Once that is done, we should be able to fully remove these classes from the public API in 0.5.0 (we can still provide a conversion utility in the HDF5Driver for example, it would just be a private method instead of being part of the public, user-facing API).