Revert "Add a SCOPED_CRASH_KEY to check if it was a browser initiated or not"

This reverts commit https://crrev.com/c/6507286.

Reason for revert:
The investigation using these crash keys is complete. The root cause
identified in crbug.com/411855273 has already been fixed, making these
temporary crash keys and associated code changes no longer necessary.

Original change's description:
> Add a SCOPED_CRASH_KEY to check if it was a browser initiated or not
>
> After starting experimenting with DumpWithoutCrashing mode of
> kAvoidUnnecessaryBeforeUnloadCheckSync feature, we received the
> following DumpWithoutCrashing report.
>
> https://crbug.com/411855273
>
> All the reports seemed to come from CSP errors for iframe navigation
> (the src was always a data url); which is a renderer initiated
> navigation. This CL confirms it.

Bug: 411855273
Bug: 396998476
Change-Id: Ice3f61755130c5196106eaf140d8f15b6a6b2e8c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7596939
Commit-Queue: Minoru Chikamune <chikamune@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1589195}