Remove support for OpenSSL 1.0.1

Here are some notes about this change:
- As X509_get_signature_nid() should always exist (OpenSSL and
LibreSSL), hence HAVE_X509_GET_SIGNATURE_NID is now gone.
- OPENSSL_API_COMPAT is bumped to 0x10002000L.
- One comment related to 1.0.1e introduced by 74242c2 is removed.

Upstream OpenSSL still provides long-term support for 1.0.2 in a closed
fashion, so removing it is out of scope for a few years, at least.

Reviewed-by: Jacob Champion, Daniel Gustafsson
Discussion: https://postgr.es/m/ZG3JNursG69dz1lr@paquier.xyz

src/interfaces/libpq/fe-auth-scram.c

@@ -401,7 +401,7 @@ build_client_first_message(fe_scram_state *state)
 		Assert(conn->ssl_in_use);
 		appendPQExpBufferStr(&buf, "p=tls-server-end-point");
 	}
-#ifdef HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
+#ifdef USE_SSL
 	else if (conn->channel_binding[0] != 'd' && /* disable */
 			 conn->ssl_in_use)
 	{
@@ -474,7 +474,7 @@ build_client_final_message(fe_scram_state *state)
 	 */
 	if (strcmp(state->sasl_mechanism, SCRAM_SHA_256_PLUS_NAME) == 0)
 	{
-#ifdef HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
+#ifdef USE_SSL
 		char	   *cbind_data = NULL;
 		size_t		cbind_data_len = 0;
 		size_t		cbind_header_len;
@@ -540,9 +540,9 @@ build_client_final_message(fe_scram_state *state)
 		appendPQExpBufferStr(&conn->errorMessage,
 							 "channel binding not supported by this build\n");
 		return NULL;
-#endif							/* HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH */
+#endif							/* USE_SSL */
 	}
-#ifdef HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
+#ifdef USE_SSL
 	else if (conn->channel_binding[0] != 'd' && /* disable */
 			 conn->ssl_in_use)
 		appendPQExpBufferStr(&buf, "c=eSws");	/* base64 of "y,," */

src/interfaces/libpq/fe-auth.c

@@ -478,7 +478,7 @@ pg_SASL_init(PGconn *conn, int payloadlen)
 			{
 				/* The server has offered SCRAM-SHA-256-PLUS. */
 
-#ifdef HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
+#ifdef USE_SSL
 				/*
 				 * The client supports channel binding, which is chosen if
 				 * channel_binding is not disabled.

src/interfaces/libpq/fe-secure-openssl.c

@@ -364,7 +364,6 @@ pgtls_write(PGconn *conn, const void *ptr, size_t len)
 	return n;
 }
 
-#if defined(HAVE_X509_GET_SIGNATURE_NID) || defined(HAVE_X509_GET_SIGNATURE_INFO)
 char *
 pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len)
 {
@@ -439,7 +438,6 @@ pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len)
 
 	return cert_hash;
 }
-#endif							/* HAVE_X509_GET_SIGNATURE_NID */
 
 /* ------------------------------------------------------------ */
 /*						OpenSSL specific code					*/
@@ -1826,8 +1824,6 @@ PQsslAttribute(PGconn *conn, const char *attribute_name)
  *
  * These functions are closely modelled on the standard socket BIO in OpenSSL;
  * see sock_read() and sock_write() in OpenSSL's crypto/bio/bss_sock.c.
- * XXX OpenSSL 1.0.1e considers many more errcodes than just EINTR as reasons
- * to retry; do we need to adopt their logic for that?
  */
 
 #ifndef HAVE_BIO_GET_DATA

src/interfaces/libpq/libpq-int.h

@@ -833,14 +833,8 @@ extern ssize_t pgtls_write(PGconn *conn, const void *ptr, size_t len);
  *
  * NULL is sent back to the caller in the event of an error, with an
  * error message for the caller to consume.
- *
- * This is not supported with old versions of OpenSSL that don't have
- * the X509_get_signature_nid() function.
  */
-#if defined(USE_OPENSSL) && (defined(HAVE_X509_GET_SIGNATURE_NID) || defined(HAVE_X509_GET_SIGNATURE_INFO))
-#define HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
 extern char *pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len);
-#endif
 
 /*
  * Verify that the server certificate matches the host name we connected to.