DOC: Empty backends page is confusing

https://aida.readthedocs.io/en/latest/aida_backends.html

There is nothing after colon. Add "TBA", real backend doc, or hide the page for now.

Read the linked aida_backends.html page first and locate the documentation source that produces its empty section. Confirm with maintainers whether the intended resolution is “TBA,” real backend documentation, or hiding the page; done means the published page no longer presents an empty section.

Written by the indexing model from the issue text.