Revert "desk_templates: Prevent exiting overview when dialogs close"

This reverts commit 66ee274344ef85f9ee4f482c3c01eeb59343b624.

Reason for revert: Suspected for making DesksTemplatesTest.UnsupportedAppsDialog flaky - see bug

Bug: 1270150

Original change's description:
> desk_templates: Prevent exiting overview when dialogs close
>
> Currently when users accept or cancel a dialog it will close overview
> due to the dialog's window being activated and then destroyed, making
> the activation client activate the next activatable window.
>
> This CL prevents this by making the OverviewSession not end overview
> when a dialog loses activation (it already does this when the dialog
> gains activation).
>
> Test: modified
> Bug: 1269444
> Change-Id: Ia527e6ce9d69bcf6be77987a27af3467a0aadac8
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3275745
> Commit-Queue: Jeremy Chinsen <chinsenj@chromium.org>
> Reviewed-by: Sammie Quon <sammiequon@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#941292}

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1269444
Change-Id: I8e265b381115a41d84c8fb0970d8b5939352caa4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3279329
Owners-Override: Trent Apted <tapted@chromium.org>
Auto-Submit: Trent Apted <tapted@chromium.org>
Reviewed-by: Ben Reich <benreich@chromium.org>
Commit-Queue: Ben Reich <benreich@chromium.org>
Cr-Commit-Position: refs/heads/main@{#941544}