This reverts commit 60e9b503.

Reason for revert: Speculative revert for https://luci-milo.appspot.com/ui/inv/build-8807661142690641489/test-results?q=conformance%2Fogles%2FGL%2FgreaterThanEqual%2FgreaterThanEqual_001_to_008.html

Original change's description:
> cppgc: Consistently treat sentinel pointer as live
>
> Sentinel pointers would be treated as live by the GC (through
> `HandleWeak()` but would be treated as dead when checked explicitly
> through the `LivenessBroker` in e.g. custom callbacks.
>
> Treat sentinel pointers as live consistently across all callsites
> and weak types.
>
> Change-Id: I9a4c096ddac1a111df808f3683325b55e7597eea
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3782800
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Omer Katz <omerkatz@chromium.org>
> Reviewed-by: Anton Bikineev <bikineev@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#81916}

Change-Id: Ic1ea0655499ae2e4ae7252fda7158d809e4970ca
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3783992
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81929}