Revert "[AUSM] Show Toast"

This reverts commit 51808635dd91cfcbda53fcfc001a7fe837135081.

Reason for revert: Failure on linux-win-cross-rel bot https://ci.chromium.org/ui/p/chromium/builders/ci/linux-win-cross-rel

Bug: b:428014205
Original change's description:
> [AUSM] Show Toast
>
> This CL adds the necessary wiring such that the toast shows under the
> correct conditions.
>
> Demo: https://screencast.googleplex.com/cast/NjA2NTk0MzQxNDMwODg2NHw2NTEyMmJlZS0yZA
>
> DD: go/toast-one-pager
>
> Bug: b:428014205
> Change-Id: I105845dae5e3f83a712f0489a85318608f646e58
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6732160
> Reviewed-by: Kevin Graney <kmg@google.com>
> Commit-Queue: Aashna Sheth <aashnas@google.com>
> Cr-Commit-Position: refs/heads/main@{#1490390}

Bug: b:428014205
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: Iabddda2042e9c0c115cde1d3a1bedcce99ea7204
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6780080
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Ken Okada <kenoss@chromium.org>
Owners-Override: Ken Okada <kenoss@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1490519}