packet_crypt: fix unused variable compiler warning

The local `rc` variable here is never set.  Fix a warning that is
emitted due to `-Wunused-variable`.

Signed-off-by: Jon Simons <jon@jonsimons.org>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

src/packet_crypt.c

@@ -102,7 +102,6 @@ int ssh_packet_decrypt(ssh_session session,
                        size_t encrypted_size)
 {
     struct ssh_cipher_struct *crypto = session->current_crypto->in_cipher;
-    int rc;
 
     if (encrypted_size <= 0) {
         return SSH_ERROR;