openssh: Don't include an unused EVP_CIPHER_CTX_get_iv() stub

This stub isn't actually used on modern versions of OpenSSL for which
OpenSSH uses EVP_CIPHER_CTX_get_updated_iv instead via a wrapper macro.

However, the wrapper macro conflicted with the existing namespace
macro triggering an error on GCC:

In file included from crypto/openssh/sshd-session.c:65:
crypto/openssh/openbsd-compat/openssl-compat.h:71:11: error: "EVP_CIPHER_CTX_get_iv" redefined [-Werror]
   71 | #  define EVP_CIPHER_CTX_get_iv EVP_CIPHER_CTX_get_updated_iv
      |           ^~~~~~~~~~~~~~~~~~~~~
In file included from <command-line>:
crypto/openssh/ssh_namespace.h:12:9: note: this is the location of the previous definition
   12 | #define EVP_CIPHER_CTX_get_iv                   Fssh_EVP_CIPHER_CTX_get_iv
      |         ^~~~~~~~~~~~~~~~~~~~~

The error was masked on clang due to MIT krb5 adding a blanket
-Wno-macro-redefined.  Building sshd-session without Kerberos support
was sufficient to trigger a warning from clang.

Reviewed by:	des
Differential Revision:	https://reviews.freebsd.org/D51810

crypto/openssh/openbsd-compat/libressl-api-compat.c

@@ -26,6 +26,7 @@
 #include <openssl/evp.h>
 
 #ifndef HAVE_EVP_CIPHER_CTX_GET_IV
+# ifndef HAVE_EVP_CIPHER_CTX_GET_UPDATED_IV
 int
 EVP_CIPHER_CTX_get_iv(const EVP_CIPHER_CTX *ctx, unsigned char *iv, size_t len)
 {
@@ -44,14 +45,15 @@ EVP_CIPHER_CTX_get_iv(const EVP_CIPHER_CTX *ctx, unsigned char *iv, size_t len)
 	if (len != 0) {
 		if (iv == NULL)
 			return 0;
-# ifdef HAVE_EVP_CIPHER_CTX_IV
+#  ifdef HAVE_EVP_CIPHER_CTX_IV
 		memcpy(iv, EVP_CIPHER_CTX_iv(ctx), len);
-# else
+#  else
 		memcpy(iv, ctx->iv, len);
-# endif /* HAVE_EVP_CIPHER_CTX_IV */
+#  endif /* HAVE_EVP_CIPHER_CTX_IV */
 	}
 	return 1;
 }
+# endif /* HAVE_EVP_CIPHER_CTX_GET_UPDATED_IV */
 #endif /* HAVE_EVP_CIPHER_CTX_GET_IV */
 
 #ifndef HAVE_EVP_CIPHER_CTX_SET_IV

crypto/openssh/ssh_namespace.h

@@ -9,7 +9,6 @@
 #define Blowfish_initstate			Fssh_Blowfish_initstate
 #define Blowfish_stream2word			Fssh_Blowfish_stream2word
 #define Decode					Fssh_Decode
-#define EVP_CIPHER_CTX_get_iv			Fssh_EVP_CIPHER_CTX_get_iv
 #define EVP_CIPHER_CTX_set_iv			Fssh_EVP_CIPHER_CTX_set_iv
 #define Encode					Fssh_Encode
 #define Hide					Fssh_Hide