ff_ffplay: remove ffp_set_playback_async_statistic declare

ijkmedia/ijkplayer/ff_ffplay.c

@@ -3316,7 +3316,6 @@ static AVDictionary **ffp_get_opt_dict(FFPlayer *ffp, int opt_category)
     }
 }
 
-static void ffp_set_playback_async_statistic(FFPlayer *ffp, int64_t buf_backwards, int64_t buf_forwards, int64_t buf_capacity);
 static int app_func_event(AVApplicationContext *h, int message ,void *data, size_t size)
 {
     if (!h || !h->opaque || !data)