Investigate removing nested option in checkboxes component

[andysellick]

We have a nested option for the checkboxes component, which looks like this:

The Design System component on which this component is based doesn't have this option - we added it as a custom option a few years ago. There are some possible accessibility concerns:

• no hierarchy present for screen reader users to understand that nested checkboxes belong to a parent (was previously in a list, but we've updated the markup to match the DS component, which uses DIV elements instead of lists)
• no indication for screen reader users that changing nested checkboxes can select/deselect parent checkboxes (is this a problem?)

It's not currently clear how widely used the nested option is. One usage is when choosing 'Get emails' on some finders, which often shows something like this:

This could potentially be a non-nested list with an 'all' option appended.

Other uses to investigate:

• collections-publisher (1)
• content-publisher (1)
• datagovuk_find (1)
• finder-frontend (2)
• release (1)
• signon (7)
• smart-answers (1)
• travel-advice-publisher (3)
• whitehall (21)

If we weren't using the nested option we could remove it and save ourselves a chunk of JavaScript and the general maintenance overhead, but further investigation is needed.