In preparation for cleaning up PipelineData to use a MachineGraph
where appropriate, move the dead node up to MachineGraph.

R=ahaas@chromium.org

Bug: v8:7721
Change-Id: I3f9d456aef7cf4d80adbc93ae938636ffcc3712d
Reviewed-on: https://chromium-review.googlesource.com/1046828
Commit-Queue: Ben Titzer <titzer@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53037}