Simplify Numba usage; numba-fy temperature.fuentes

[kandersolar]

• Closes reevaluate numba minimum, usage patterns in spa.py #1060
• I am familiar with the contributing guidelines
• Tests added
• Updates entries to docs/sphinx/source/api.rst 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`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels and Milestone are assigned to the Pull Request and linked Issue.
• Address TODOs in code
• Update benchmarks to be backwards compatible (e.g. PVLIB_USE_NUMBA)
• Scrub nrel_numpy/nrel_numba from tutorial notebooks

[kandersolar]

I think this could use another set of eyes -- I'm having some trouble wrapping my head around testing with and without numba and I'm not sure what I'm doing for the SPA tests makes sense.

[cwhanse]

Suggested change

	warnings.warn("The 'how' parameter is deprecated; numba is now used "
	"automatically if it is available.",
	warnings.warn("The 'how' parameter is deprecated; numba is now used "
	"automatically if it is available, otherwise numpy is used.",

[cwhanse]

The use of numba is beyond me. The spa interface is better without how, I think.