Revert "Declare Chrome OS Account Manager for field trial testing"

This reverts commit cd74eba0.

Reason for revert: Speculative revert due to DCHECK failures in linux-chromeos-dbg

Bug: 929785

Original change's description:
> Declare Chrome OS Account Manager for field trial testing
> 
> Bug: 816954
> Change-Id: I4ee640075af0948cbb8b5bfcc127123348cad98b
> Reviewed-on: https://chromium-review.googlesource.com/c/1426779
> Commit-Queue: Kush Sinha <sinhak@chromium.org>
> Reviewed-by: Ilya Sherman <isherman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#629940}

TBR=isherman@chromium.org,sinhak@chromium.org

Change-Id: I3d89e1e798164bc774c084e867e7cbd969487063
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 816954
Reviewed-on: https://chromium-review.googlesource.com/c/1459326Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630035}

testing/variations/fieldtrial_testing_config.json

@@ -1741,21 +1741,6 @@
             ]
         }
     ],
-    "EnableChromeOSAccountManager": [
-        {
-            "platforms": [
-                "chromeos"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "ChromeOSAccountManager"
-                    ]
-                }
-            ]
-        }
-    ],
     "EnableCsrssLockdown": [
         {
             "platforms": [