Prepare to replace VideoLayerFrameId with int64_t.

Bug: webrtc:12206
Change-Id: I10bfdefbc95a79e0595956c1a0e688051da6d2b9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/207180
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33265}

api/video/video_stream_decoder_create_unittest.cc

@@ -21,7 +21,6 @@ class NullCallbacks : public VideoStreamDecoderInterface::Callbacks {
  public:
   ~NullCallbacks() override = default;
   void OnNonDecodableState() override {}
-  void OnContinuousUntil(const video_coding::VideoLayerFrameId& key) override {}
   void OnDecodedFrame(VideoFrame frame,
                       const VideoStreamDecoderInterface::Callbacks::FrameInfo&
                           frame_info) override {}