EVP_HPKE_KEM: Clean up unused fields in evp_hpke_key_st

Finishes some previously-missed cleanup.

Update-Note: This changes the internal structure of EVP_HPKE_KEY, which
callers should not access or modify.

Bug: 535883377
Change-Id: I74c0abd556ef0a82c7d7f9036c1c34b86a6a6964
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/104708
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: Lily Chen <chlily@google.com>
Presubmit-BoringSSL-Verified: boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com>

crypto/hpke/hpke.cc

diff --git a/crypto/hpke/hpke.cc b/crypto/hpke/hpke.cc
index fee1405..70487fa 100644
--- a/crypto/hpke/hpke.cc
+++ b/crypto/hpke/hpke.cc
@@ -857,8 +857,6 @@
 
 int EVP_HPKE_KEY_copy(EVP_HPKE_KEY *dst, const EVP_HPKE_KEY *src) {
   dst->kem = src->kem;
-  OPENSSL_memcpy(dst->private_key, src->private_key, sizeof(src->private_key));
-  OPENSSL_memcpy(dst->public_key, src->public_key, sizeof(src->public_key));
   dst->pkey = EVP_PKEY_dup_ref(src->pkey);
   return 1;
 }

include/openssl/hpke.h

diff --git a/include/openssl/hpke.h b/include/openssl/hpke.h
index bb91594..6cc8bbd 100644
--- a/include/openssl/hpke.h
+++ b/include/openssl/hpke.h
@@ -420,14 +420,6 @@
 
 struct evp_hpke_key_st {
   const EVP_HPKE_KEM *kem;
-  uint8_t private_key[EVP_HPKE_MAX_PRIVATE_KEY_LENGTH];
-  uint8_t public_key[EVP_HPKE_MAX_PUBLIC_KEY_LENGTH];
-
-  // `pkey`, if non-null, takes precedence over `private_key` and `public_key`,
-  // which are left unused. Otherwise `private_key` and `public_key` are used
-  // instead.
-  // TODO(crbug.com/535883377): Unify EVP_HPKE_KEM and EVP_KEM for all supported
-  // HPKE KEMs.
   EVP_PKEY *pkey;
 };