Delete GCMTokenInvalidAfterDays fieldtrial testing config

now that the feature has been rolled out everywhere.

Bug: 814376
Change-Id: I14e8463cfc0a948f6e41b50990a6f1f759aa2646
Reviewed-on: https://chromium-review.googlesource.com/1069014Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Mugdha Lakhani <nator@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561005}

testing/variations/fieldtrial_testing_config.json

@@ -1414,25 +1414,6 @@
             ]
         }
     ],
-    "GCMTokenInvalidAfterDays": [
-        {
-            "platforms": [
-                "linux",
-                "mac",
-                "win",
-                "chromeos",
-                "ios"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "GCMTokenInvalidAfterDays"
-                    ]
-                }
-            ]
-        }
-    ],
     "GoogleBrandedContextMenu": [
         {
             "platforms": [