evloop: fix docs for threadpool_register_reply_event

Commit 6a5f62f6 ultimately didn't
include the base argument, and the callback is named cb.

src/lib/evloop/workqueue.c

@@ -622,8 +622,8 @@ reply_event_cb(evutil_socket_t sock, short events, void *arg)
     tp->reply_cb(tp);
 }
 
-/** Register the threadpool <b>tp</b>'s reply queue with the libevent
- * mainloop of <b>base</b>. If <b>tp</b> is provided, it is run after
+/** Register the threadpool <b>tp</b>'s reply queue with Tor's global
+ * libevent mainloop. If <b>cb</b> is provided, it is run after
  * each time there is work to process from the reply queue. Return 0 on
  * success, -1 on failure.
  */

src/lib/evloop/workqueue.h

@@ -63,7 +63,6 @@ replyqueue_t *threadpool_get_replyqueue(threadpool_t *tp);
 replyqueue_t *replyqueue_new(uint32_t alertsocks_flags);
 void replyqueue_process(replyqueue_t *queue);
 
-struct event_base;
 int threadpool_register_reply_event(threadpool_t *tp,
                                     void (*cb)(threadpool_t *tp));