Revert "Cross-origin support for window.fence.reportEvent()."

This reverts commit 280fe80c.

Reason for revert: Consistent failures: blink_wpt_tests on *

Example:
virtual/fenced-frame-mparch/external/wpt/fenced-frame/fence-report-event-cross-origin-urn-iframe.https.html

Regression ranges: chromium/src: 1282145 - 1282166

Bug: crbug.com/332755365

Original change's description:
> Cross-origin support for window.fence.reportEvent().
>
> Third-party ad serving (3PAS) lets advertisers manage ads across
> different bidding platforms. However, the event-level reporting API
> (reportEvent()) currently prevents direct reporting from documents that
> are cross-origin to the root ad frame's fenced frame config's mapped
> URL, limiting this functionality for the 3PAS use case. This CL extends
> the reportEvent() API to support this use case.
>
> To allow cross-origin reporting while still preserving privacy, both the
> ad frame and the 3PAS subframe must explicitly opt in. The ad frame opts
> in using a new `Allow-Cross-Origin-Event-Reporting` response header,
> while the 3PAS subframe opts in by calling reportEvent() with
> `crossOriginExposed=true`. If both opt-ins are present, then the
> reportEvent() call from the 3PAS document will succeed.
>
> This CL adds histograms to track how many beacons are sent from
> documents that are same-origin and cross-origin to the fenced frame
> config's mapped url.
>
> This CL also expands the fenced frame WPT system to support
> content-initiated navigations of fenced frame contexts to cross-origin
> URLs.
>
> Change-Id: I4e895bec4cb77604e2017cfc67b496d59863a30b
> Bug: 331844131
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5403108


> Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
> Reviewed-by: Ben Kelly <wanderview@chromium.org>
> Reviewed-by: Dominic Farolino <dom@chromium.org>
> Reviewed-by: Garrett Tanzer <gtanzer@chromium.org>
> Commit-Queue: Liam Brady <lbrady@google.com>
> Cr-Commit-Position: refs/heads/main@{#1282086}

Bug: 331844131
Change-Id: I2fa4be5108ded57fa3c7e6675031a52ddf39a574
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5422053


Reviewed-by: Solomon Kinard <solomonkinard@google.com>
Auto-Submit: Solomon Kinard <solomonkinard@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Solomon Kinard <solomonkinard@google.com>
Commit-Queue: Solomon Kinard <solomonkinard@google.com>
Cr-Commit-Position: refs/heads/main@{#1282260}