Revert "Send dropEffect attribute on drag and drop events"

This reverts commit 0542983115c4ccbaa2b1dd15faff2675d520bbeb.

Reason for revert: Lots of CrossSiteSubframe/DragAndDropBrowserTest tests are broken. 
https://ci.chromium.org/ui/p/chromium/builders/ci/Linux%20ChromiumOS%20MSan%20Tests

Bug: 442927728,434151262
Original change's description:
> Send dropEffect attribute on drag and drop events
>
> This CL implements the dropEffect attribute in the dataTransfer property
> in drag and drop event to match the spec.
> https://html.spec.whatwg.org/multipage/dnd.html
>
> The attribute is currently not being set, defaulting to "none" on all
> events.
>
> Many existing tests were updated to pass with the new implementation.
> Notably, the default dropEffect for some "effectAllowed" attributes has
> been changed to match the defaults in the table found in "6.11.4 The
> DragEvent interface" in the spec. (defaulting to copy whenever copy is
> available, and to link if link is available)
>
> Bug: 434151262
> Change-Id: Iaeaa7e0e4b9a44e89379b6adf72650ab89fe3dd3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6803149
> Commit-Queue: Gaston Rodriguez <gastonr@microsoft.com>
> Reviewed-by: Avi Drissman <avi@chromium.org>
> Reviewed-by: Olga Gerchikov <gerchiko@microsoft.com>
> Reviewed-by: Kent Tamura <tkent@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1509844}

Bug: 442927728,434151262
Change-Id: I6eb9f9f6d79025b691e5ae77ed4090ad76b6f99a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6915315
Commit-Queue: Jiacheng Guo <gjc@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Jiacheng Guo <gjc@google.com>
Cr-Commit-Position: refs/heads/main@{#1510766}