Remove deprecated `pvsystem.sapm_spectral_loss`

[RDaxini]

• [X] Closes #2243
• [X] I am familiar with the contributing guidelines
• [X] Tests ~added~ removed
• [ ] Updates entries in docs/sphinx/source/reference for API changes.
• [ ] Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`). Wait for 12.0?
• [ ] New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• [x] Pull request is nearly complete and ready for detailed review.
• [ ] Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

I am not super familiar with deprecations so please correct me if I have misunderstood something here or even missed an existing PR for this...