libavformat/utils.c: silence final MythTV warning

No functional change, but AVStream.codec was removed in FFmpeg 5.0.

This should enable it to compile with FFmpeg 5.0, since it will then be
not compiled.

mythtv/external/FFmpeg/libavformat/utils.c

@@ -5952,12 +5952,16 @@ void av_remove_stream(AVFormatContext *s, int id, int remove_ts) {
 
         av_log(NULL, AV_LOG_DEBUG, "av_remove_stream 0x%x\n", id);
 
+#if FF_API_LAVF_AVCTX
+FF_DISABLE_DEPRECATION_WARNINGS
         /* close codec context */
         codec_ctx = s->streams[i]->codec;
         if (codec_ctx->codec) {
             avcodec_close(codec_ctx);
             av_free(codec_ctx);
         }
+FF_ENABLE_DEPRECATION_WARNINGS
+#endif
 #if 0
         /* make sure format context is not using the codec context */
         if (&s->streams[i] == s->cur_st) {