Don't use non or just quazi public API

[bsipocz]

The tutorials should avoid using non user facing API, e.g. functionality from anything from astroquery.utils (maybe except TAP+ that already has it's own narrative docs, though also mostly destined to be used in other modules). These utilities are clearly listed under Developer Documentation here: https://astroquery.readthedocs.io/en/latest/index.html#developer-documentation

E.g. the FITS-cube tutorials uses TableList while it shouldn't.

[kelle]

This note should be added to the dev docs. https://github.com/astropy-learn/dev-guide/