Can we remove `access_to_span()`?

[Iain-S]

rctab-api/rctab/routers/frontend.py

Line 81 in d27a908

def access_to_span(status: bool) -> str:

It doesn't appear that the access_to_span() does anything meaningful, though we do call it in a handful of places.
If it is a vestigial remnant of a previous authorisation model, we can remove it.