Tablist example should be updated, maring as legacy or removing radio button POC

[RA11y1]

For the tabs widget the ADG already references the WAI-ARIA Authoring practices, which contains examples for tablists with manual and auto activation: WAI ARIA Tabs
There already is a section under the tablist widget page for an ARIA POC, which is marked with TODO: Example Tablist

The tablists from the WAI-ARIA patterns page work robustly enough on different browsers and screen readers and can therefore be used here. The only thing that should be improved from the WAI ARIA patterns is switching from an display: inline-block; to a display: block; on the tab items. The inline-block prevents the screen reader NVDA from navigating through the tablist via browse mode. Since the browse mode prevents auto selection of tabs on focus, I would suggest only incorporating the manual tab list.

The example using radio buttons is currently the only example present. However, this is now considered outdated and should either get marked as legacy or get removed: tablist with radio buttons

In the chapter "Widgets simply working for all" the tablist with radio buttons is mentioned as an example: Widgets simply working for all
Like the page itself mentions, other than tablists there isn't really another example that illustrates the message well, therefore I am not sure if this page is still relevant.

@backflip @rudigier @christophdubach let me know if there should be anything missing.

[rudigier]

We also can remove the legacy example with radio buttons. But here is the first draft.
#470