Turn SSH-1 ciphers into a classoid.

The interchangeable system of SSH-1 ciphers previously followed the
same pattern as the backends and the public-key algorithms, in that
all the clients would maintain two separate pointers, one to the
vtable and the other to the individual instance / context. Now I've
merged them, just as I did with those other two, so that you only cart
around a single pointer, which has a vtable pointer inside it and a
type distinguishing it from an instance of any of the other
interchangeable sets of algorithms.

ssh.c

@@ -2914,10 +2914,9 @@ static void do_ssh1_login(void *vctx)
     sfree(s->rsabuf);
 
     {
-        const struct ssh_cipher *cipher =
-            (s->cipher_type == SSH_CIPHER_BLOWFISH ? &ssh_blowfish_ssh1 :
-             s->cipher_type == SSH_CIPHER_DES ? &ssh_des :
-             &ssh_3des);
+        const struct ssh1_cipheralg *cipher =
+            (s->cipher_type == SSH_CIPHER_BLOWFISH ? &ssh1_blowfish :
+             s->cipher_type == SSH_CIPHER_DES ? &ssh1_des : &ssh1_3des);
         ssh1_bpp_new_cipher(ssh->bpp, cipher, ssh->session_key);
         logeventf(ssh, "Initialised %s encryption", cipher->text_name);
     }