Remove FormControlsRefresh entry from testing config.

The server-side config shows that this on only old versions of Chrome.
Plus, as of [1] the feature is enabled on TOT for desktop.

[1] crrev.com/c/2063530

Bug: 1126640
Change-Id: I17afe09c1da894411f66ef7791a1c1edc441d00a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2632126
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Reviewed-by: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844160}

testing/variations/fieldtrial_testing_config.json

@@ -3148,24 +3148,6 @@
             ]
         }
     ],
-    "FormControlsRefresh": [
-        {
-            "platforms": [
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "FormControlsRefresh"
-                    ]
-                }
-            ]
-        }
-    ],
     "FreezeBackgroundTabOnNetworkIdle": [
         {
             "platforms": [