audio filters: remove old filter_NewAudioBuffer()
chroma: add avutil version check for YUV422P9LE/BE (fix #8249)

swscale is broken on systems with disable-avcodec (not meeting avcodec
version requirement).
According to ffmpeg commit e06be9eccdc969a9fd2736c2daf37c2fbccae37f
those chromas have been introduced after avutil 51.12.0.