Revert "avcodec/vp9_superframe_bsf: cache packets by creating new references rather than moving them"

This reverts commit 7a02b364.

The packet fetched by ff_bsf_get_packet() and ff_bsf_get_packet_ref()
is now guaranteed to be reference counted.
Reviewed-by: wm4 <nfxjfg@googlemail.com>
Signed-off-by: James Almer <jamrial@gmail.com>