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/+/2523177Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824892}

testing/variations/fieldtrial_testing_config.json

@@ -2562,21 +2562,6 @@
             ]
         }
     ],
-    "EnableCloseAllTabsConfirmation": [
-        {
-            "platforms": [
-                "ios"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "EnableCloseAllTabsConfirmation"
-                    ]
-                }
-            ]
-        }
-    ],
     "EnableContextMenuPerformanceHints": [
         {
             "platforms": [