avformat/mux: Remove check for AVFMT_ALLOW_FLUSH

Due to the bump it is now certain that all devices
that support flushing have the proper internal flag set.
(Notice that the check for LIBAVFORMAT_VERSION was wrong.)

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/mux.c

@@ -1236,13 +1236,7 @@ int av_write_frame(AVFormatContext *s, AVPacket *in)
     int ret;
 
     if (!in) {
-#if FF_API_ALLOW_FLUSH || LIBAVFORMAT_VERSION_MAJOR >= 61
-        // Hint: The pulse audio output device has this set,
-        // so we can't switch the check to FF_OFMT_FLAG_ALLOW_FLUSH immediately.
-        if (s->oformat->flags & AVFMT_ALLOW_FLUSH) {
-#else
         if (ffofmt(s->oformat)->flags_internal & FF_OFMT_FLAG_ALLOW_FLUSH) {
-#endif
             ret = ffofmt(s->oformat)->write_packet(s, NULL);
             flush_if_needed(s);
             if (ret >= 0 && s->pb && s->pb->error < 0)