This also removes the old poly1305_auth interface, as it no longer serves any
function. The new Poly1305 class based interface is more modern and safe.
This concludes backport of core#27993
https://github.com/bitcoin/bitcoin/pull/27993/commits/4e5c933f6a40c07d1c68115f7979b89a5b2ba580
Depends on D19015