remove some (confusing) dead code

src/or/router.c

@@ -85,7 +85,6 @@ set_onion_key(crypto_pk_env_t *k)
   tor_mutex_acquire(key_lock);
   crypto_free_pk_env(onionkey);
   onionkey = k;
-  onionkey_set_at = time(NULL);
   tor_mutex_release(key_lock);
   mark_my_descriptor_dirty("set onion key");
 }