This avoids avpriv functions from lavc/opus/parse.c
(which parse way more than we need, necessitating
parsing the extradata).
It furthermore makes the output of the muxer consistent,
i.e. no longer depending upon whether the Opus parser
or decoder are enabled (the avpriv functions would just
return AVERROR(ENOSYS)).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
