Revert "Use base::apple::Owned[frameworktype] for ui::PlatformEvent"

This reverts commit 326a3f7d.

Reason for revert: Might be cause of https://crbug.com/1449023

Original change's description:
> Use base::apple::Owned[frameworktype] for ui::PlatformEvent
>
> base::apple::Owned[frameworktype] is a new way to easily generate
> owning wrapper classes for framework types. This CL switches
> ui::PlatformEvent to use it, and does cleanup.
>
> This unlocks the ability to convert ui/events/ to use ARC.
>
> Bug: 1443009
> Bug: 1433041
> Bug: 1280317
> Change-Id: Ib1ffd2f54aa1ba641eebbabe3ed4349b026650f3
> Include-Ci-Only-Tests: true
> Cq-Include-Trybots: luci.chromium.try:ios-blink-dbg-fyi
> Cq-Include-Trybots: luci.chrome.try:mac-chrome
> Validate-Test-Flakiness: skip
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4562796


> Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
> Auto-Submit: Avi Drissman <avi@chromium.org>
> Reviewed-by: Mark Mentovai <mark@chromium.org>
> Commit-Queue: Avi Drissman <avi@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1149240}

Bug: 1443009
Bug: 1433041
Bug: 1280317
Bug: 1449023
Change-Id: I555fed7f7e764b0721275f9224f6721b02c219eb
Cq-Include-Trybots: luci.chromium.try:ios-blink-dbg-fyi
Cq-Include-Trybots: luci.chrome.try:mac-chrome
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4566548
Auto-Submit: Avi Drissman <avi@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1149427}