This reverts commit cf1fad58.

Reason for revert: Breaks web tests: https://ci.chromium.org/p/v8/builders/ci/V8%20Blink%20Linux%20Debug/2684

Original change's description:
> [tooling] Keep track of idle state even when we aren't profiling
> 
> It isn't expensive to set this enum on the isolate and we only call
> this in chrome when the ThreadDebugger is enabled anyway.
> 
> This means we have a correct idle state to use with the upcoming
> CDP event which emits the thread state.
> 
> Bug: chromium:1025490
> Change-Id: Ia555ac8c401d0ad7c72d4cbc442be388ce166131
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2036087
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Commit-Queue: Peter Marshall <petermarshall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#66125}

TBR=yangguo@chromium.org,petermarshall@chromium.org

Change-Id: I3823197974a2e683364f56819de6ea33dbb8b296
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1025490
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2037441Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66133}