The idea behind last_pkt_props was to store the properties of the last packet
fed to the decoder. Any sort of queueing required by CODEC_CAP_DELAY decoders
that consume several packets before they start outputting frames should be done
by the decoders in question. An example of this is libdav1d.

This is required for the following commits that will fix last_pkt_props in
frame threading scenarios, as well as maintain its contents during flush.

This revers commit 022a12b3.
Signed-off-by: James Almer <jamrial@gmail.com>