Remove SSL_CTX_get_client_cert_cb.

This is never used. Removing it allows us to implement the old callback
using the new one.

Change-Id: I4be70cc16e609ce79b51836c19fec565c67ff3d6
Reviewed-on: https://boringssl-review.googlesource.com/12689
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>

include/openssl/ssl.h

@@ -3465,11 +3465,6 @@ OPENSSL_EXPORT void SSL_CTX_set_client_cert_cb(
     SSL_CTX *ctx,
     int (*client_cert_cb)(SSL *ssl, X509 **out_x509, EVP_PKEY **out_pkey));
 
-/* SSL_CTX_get_client_cert_cb returns the callback set by
- * |SSL_CTX_set_client_cert_cb|. */
-OPENSSL_EXPORT int (*SSL_CTX_get_client_cert_cb(SSL_CTX *ctx))(
-      SSL *ssl, X509 **out_x509, EVP_PKEY **out_pkey);
-
 #define SSL_NOTHING 1
 #define SSL_WRITING 2
 #define SSL_READING 3

ssl/ssl_session.c

@@ -1013,11 +1013,6 @@ void SSL_CTX_set_client_cert_cb(SSL_CTX *ctx, int (*cb)(SSL *ssl,
   ctx->client_cert_cb = cb;
 }
 
-int (*SSL_CTX_get_client_cert_cb(SSL_CTX *ctx))(SSL *ssl, X509 **out_x509,
-                                                EVP_PKEY **out_pkey) {
-  return ctx->client_cert_cb;
-}
-
 void SSL_CTX_set_channel_id_cb(SSL_CTX *ctx,
                                void (*cb)(SSL *ssl, EVP_PKEY **pkey)) {
   ctx->channel_id_cb = cb;