Revert "Adds ChangeTabSwitcherPosition to Field Trial Testing Configuration"

This reverts commit 62ef43a9.

Reason for revert: Speculative revert to fix ios13-beta-simulator failures. See https://ci.chromium.org/p/chromium/builders/ci/ios13-beta-simulator/15625.
If the revert does not fix the breakage, I will put this back.

Original change's description:
> Adds ChangeTabSwitcherPosition to Field Trial Testing Configuration
> 
> 
> Bug: 1073826
> Change-Id: I378c67f926df54bd4bd75d0a64f7b241534238a7
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2208971
> Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
> Reviewed-by: Gauthier Ambard <gambard@chromium.org>
> Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#775055}

TBR=asvitkine@chromium.org,gambard@chromium.org,ewannpv@chromium.org

Change-Id: I7b4dab3b0627b5d4b6375638021eec62610c48d9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1073826
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2231591Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775305}

testing/variations/fieldtrial_testing_config.json

@@ -2888,21 +2888,6 @@
             ]
         }
     ],
-    "IOSChangeTabSwitcherPosition": [
-        {
-            "platforms": [
-                "ios"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "ChangeTabSwitcherPosition"
-                    ]
-                }
-            ]
-        }
-    ],
     "IOSCrashReportBreadcrumbs": [
         {
             "platforms": [