This reverts commit a441cbfb.

Reason for revert: causes DeepEagerCompilationPeakMemory to fail.

https://ci.chromium.org/p/v8/builders/ci/V8%20Linux/36681

Original change's description:
> [offthread] Move stress-background-compile to compiler.cc
> 
> Make --stress-background-compile a V8 flag rather than a d8 flag, so
> that it also tests unittests/cctests.
> 
> Now, with this flag, every top-level script compile (that fulfills a
> couple of restrictions) will be both main-thread and background-thread
> compiled, taking the result of the background compile. In the future,
> we'll probably want to verify that the two results are equivalent.
> 
> One of the necessary changes to allow tests to pass was to introduce a
> concept of a "temporary" script (with a temporary script id), which
> doesn't get added to the script list. This is to avoid the main-thread
> compile part of the stress-test having a debugger-visible side-effect,
> e.g. in tests that enumerate scripts. We can't just create new ids for
> such scripts, as then script-id expectation files no longer match.
> 
> Bug: chromium:1011762
> Change-Id: I500bbf2cabea762e69aca3dbae247daae71192cb
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2120541
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67332}

TBR=rmcilroy@chromium.org,leszeks@chromium.org

Change-Id: I8716b332b07fe4f394b5a32c986bbe652325582d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1011762
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2163143Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67347}