Revert "[iOS] Adds EnableCloseAllTabsConfirmation config"

This reverts commit 1ad663a1.
The name should be modified.
Reason for revert: <INSERT REASONING HERE>

Original change's description:
> [iOS] Adds EnableCloseAllTabsConfirmation config
>
> This CL adds the EnableCloseAllTabsConfirmation feature to the
> fieldtrial testing config.
>
> Bug: 1119319
> Change-Id: I197528caa2d090e2ddd6fde43b18223da49e226f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2513597


> Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
> Reviewed-by: Weilun Shi <sweilun@chromium.org>
> Reviewed-by: Ilya Sherman <isherman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#824884}

TBR=isherman@chromium.org,sweilun@chromium.org,ewannpv@chromium.org

Change-Id: Ia7ae4c6e83613b1b8f8aab8fad9279d80f727d9a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1119319
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2523177


Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824892}