Remove SKOptLearner

[basnijholt]

Description

Removes the SKOptLearner.

This continuously causes problems (e.g., https://readthedocs.org/projects/adaptive/builds/19128846/ and https://github.com/python-adaptive/adaptive/pull/333), mostly because https://scikit-optimize.github.io/stable/ is no longer maintained https://github.com/scikit-optimize/scikit-optimize.

It's not compatible with NumPy 1.24 which removed the type aliases (np.float, np.int, etc.).

Checklist

• [x] Fixed style issues using pre-commit run --all (first install using pip install pre-commit)
• [x] pytest passed

Type of change

Check relevant option(s).

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] (Code) style fix or documentation update
• [ ] This change requires a documentation update

[akhmerov]

This seems appropriate, but requires a version bump and explaining the removal in the docs. Maybe even raise a more specific import error perhaps?