Remove spurious bufferevent_free in worker.cc

stop_working() already frees the bufferevents, so don't double-free.

worker.cc

@@ -144,7 +144,6 @@ static void dpconn_event_cb(struct bufferevent *bev, short events,
     } else if (events & (BEV_EVENT_EOF|BEV_EVENT_ERROR)) {
 	fprintf(stderr, "Closing connection to dpnode\n");
 	stop_working();
-	bufferevent_free(bev);
     }
 }