Remove AutofillEnableSurfacingServerCardNickname from field trial testing config

We got full-launch approval, and already enabled by default: crrev.com/c/2334102
(We forgot to remove the field_trial config in that CL).

Bug: 1059087
Change-Id: Iae4cad3adf059ffd881a854f70198ac78c83ca7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2363923
Commit-Queue: Sujie Zhu <sujiezhu@google.com>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Siyu An <siyua@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799715}

testing/variations/fieldtrial_testing_config.json

@@ -354,27 +354,6 @@
             ]
         }
     ],
-    "AutofillEnableSurfacingServerCardNickname": [
-        {
-            "platforms": [
-                "android",
-                "android_webview",
-                "chromeos",
-                "ios",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "AutofillEnableSurfacingServerCardNickname"
-                    ]
-                }
-            ]
-        }
-    ],
     "AutofillFieldMetadata": [
         {
             "platforms": [