The allocators have been superseded by av_vdpau_bind_context().
The latter have only been added "to allow multiple forks to add
fields to the structure without breaking ABI" [1], but libav
is no more, so this is not needed any longer.
[1]: https://ffmpeg.org/pipermail/ffmpeg-devel/2013-August/146954.html
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>