crypto: remove outdated variant of ChaCha20Poly1305 AEAD

Summary:
Remove the variant of ChaCha20Poly1305 AEAD that was previously added in
anticipation of BIP324 using it. BIP324 was updated to instead use rekeying
wrappers around otherwise unmodified versions of the ChaCha20 stream cipher
and the ChaCha20Poly1305 AEAD as specified in RFC8439.

This is a partial backport of core#28008
https://github.com/bitcoin/bitcoin/pull/28008/commits/9fd085a1a49d317abcaf1492b71c48bf1a1b3007
Depends on D19016

Test Plan: ninja all check-all bench-bitcoin bitcoin-fuzzers

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D19017