Ogg: discard non-essential metadata from Vorbis header when creating extradata
The first part of the metadata, the "vendor" string, is required by
libvorbis, it will refuse to play when it is not available.
Also we do not currently parse that part into metadata so it would also
be lost if we removed it as well.
Signed-off-by: Mans Rullgard <firstname.lastname@example.org>
(cherry picked from commit 8cb3c557a9f3b24bc55325e3f64a2150b983305c)