This removes support to track the memory footprint of fully executed but
not yet finalized compilation units. It was used to throttle creation of
new tasks when the latent memory pressure of this unfinished jobs rose
above a certain threshold. Now that units no longer incur a significant
latent memory pressure, this is no longer needed.

R=clemensh@chromium.org
BUG=v8:7921

Change-Id: I3f4a563ebcb85b7aeac50f469a8a495eecf8aa3d
Reviewed-on: https://chromium-review.googlesource.com/1136291Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54435}