Remove EVP_PKEY_ASN1_METHOD and EVP_PKEY_METHOD from public headers

With EVP_PKEY and EVP_PKEY_CTX opaque, these symbols don't appear in any
public APIs anymore. Make them internal, which also opens the door to
renaming them:

- EVP_PKEY_METHOD is more accurately EVP_PKEY_CTX_METHOD
- EVP_PKEY_ASN1_METHOD is more accurately EVP_PKEY_METHOD

Or perhaps the split doesn't mean much and we should fold them together.

Change-Id: I8a0f7c2e07445dc981c7cef697263e59dba7784e
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/57885
Commit-Queue: David Benjamin <davidben@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: Bob Beck <bbe@google.com>

crypto/evp/internal.h

diff --git a/crypto/evp/internal.h b/crypto/evp/internal.h
index 71f0f95..6678c41 100644
--- a/crypto/evp/internal.h
+++ b/crypto/evp/internal.h
@@ -66,6 +66,9 @@
 #endif
 
 
+typedef struct evp_pkey_asn1_method_st EVP_PKEY_ASN1_METHOD;
+typedef struct evp_pkey_method_st EVP_PKEY_METHOD;
+
 struct evp_pkey_asn1_method_st {
   int pkey_id;
   uint8_t oid[9];

include/openssl/base.h

diff --git a/include/openssl/base.h b/include/openssl/base.h
index 190e250..a1a4309 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -419,9 +419,7 @@
 typedef struct evp_hpke_kdf_st EVP_HPKE_KDF;
 typedef struct evp_hpke_kem_st EVP_HPKE_KEM;
 typedef struct evp_hpke_key_st EVP_HPKE_KEY;
-typedef struct evp_pkey_asn1_method_st EVP_PKEY_ASN1_METHOD;
 typedef struct evp_pkey_ctx_st EVP_PKEY_CTX;
-typedef struct evp_pkey_method_st EVP_PKEY_METHOD;
 typedef struct evp_pkey_st EVP_PKEY;
 typedef struct hmac_ctx_st HMAC_CTX;
 typedef struct md4_state_st MD4_CTX;