Fix CI for RDKit and Windows

[RMeli]

This PR pins RDKit on Windows to rdkit<=2024.03.4.

rdkit/rdkit#7679
conda-forge/rdkit-feedstock#168

Additionally, unused rustworkx-only conda environments are removed.

---

CI for Windows started failing, while Linux is not affected. macOS is too slow to complete before jobs are cancelled, but locally everything works fine.

The error is the following:

ERROR tests/test_rmsd.py::test_rmsdwrapper_single_molecule[networkx-lambda_max_fast-minimize] - NameError: name 'load' is not defined
ERROR tests/test_rmsd.py::test_rmsdwrapper_single_molecule[networkx-lambda_max_fast-no_minimize] - NameError: name 'load' is not defined
ERROR tests/test_rmsd.py::test_rmsdwrapper_single_molecule[networkx-lambda_max_fallback-minimize] - NameError: name 'load' is not defined
ERROR tests/test_rmsd.py::test_rmsdwrapper_single_molecule[networkx-lambda_max_fallback-no_minimize] - NameError: name 'load' is not defined
===== 44 failed, 128 passed, 34 skipped, 4 warnings, 706 errors in 15.67s =====

and seems to appear only on Windows (and possibly only with RDKit).

[RMeli]

The import error resulting in __all__ = [] is the following:

ImportError while loading conftest 'D:\a\spyrmsd\spyrmsd\tests\conftest.py'.
tests\conftest.py:16: in <module>
    from spyrmsd import io
spyrmsd\io.py:26: in <module>
    raise e
spyrmsd\io.py:14: in <module>
    from spyrmsd.optional.rdkit import (
spyrmsd\optional\rdkit.py:6: in <module>
    import rdkit.Chem as Chem
C:\Users\runneradmin\miniconda3\envs\spyrmsd\lib\site-packages\rdkit\__init__.py:6: in <module>
    from . import rdBase
E   ImportError: DLL load failed while importing rdBase: The specified module could not be found.

[RMeli]

Pinning to rdkit<=2024.03.4 in CI (for Windows only) seems to avoid the issue.