libavutil/mem.h is unneeded since 33d18982,
the commit that introduced the new packet-based bsf API, because with
this switch the allocations were no longer performed directly, but by
av_new_packet().
Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>