chacha_poly: fix settable ctx param list

chacha_poly: fix settable ctx param list

The settable list used the generic AEAD cipher list which included
an extra parameter and omitted the IV length one.  The set ctx param call
was custom so the errant list didn't directly impact operation.

The comment about ignoring OSSL_CIPHER_PARAM_AEAD_MAC_KEY is completely bogus.
That parameter isn't accepted either here or by the shared AEAD cipher params.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
(Merged from https://github.com/openssl/openssl/pull/27534)