Revert "Do not propagate generic descriptor on receiving frame"

This reverts commit abf73de8eae90e9ac7e88ce1d52728e8102e824f.

Reason for revert: breaks downstream tests

Original change's description:
> Do not propagate generic descriptor on receiving frame
> 
> It was used only for the frame decryptor.
> Decryptor needs only raw representation that it can recreate
> in a way compatible with the new version of the descriptor.
> 
> Bug: webrtc:10342
> Change-Id: Ie098235ebb87c6f5e2af42d0022d2365cd6bfa29
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/166163
> Reviewed-by: Philip Eliasson <philipel@webrtc.org>
> Reviewed-by: Erik Språng <sprang@webrtc.org>
> Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#30501}

TBR=danilchap@webrtc.org,sprang@webrtc.org,philipel@webrtc.org

Change-Id: I6634df06ee75aa8cdfda614994ab11f7a5845c70
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:10342
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168488
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30502}

modules/video_coding/packet_buffer.cc

@@ -473,6 +473,7 @@ std::unique_ptr<RtpFrameObject> PacketBuffer::AssembleFrame(
       last_packet.video_header.content_type,    //
       first_packet.video_header,                //
       last_packet.video_header.color_space,     //
+      first_packet.generic_descriptor,          //
       RtpPacketInfos(std::move(packet_infos)),  //
       std::move(bitstream));
 }