Remove CertDualVerificationTrial entry from the testing config.

The server-side config shows that this study has ended.

Bug: 1126640
Change-Id: I49732d19f6bd15e020cda40c6745094a6ac25478
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2632205Reviewed-by: Ryan Sleevi <rsleevi@chromium.org>
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Cr-Commit-Position: refs/heads/master@{#845005}

testing/variations/fieldtrial_testing_config.json

@@ -1304,21 +1304,6 @@
             ]
         }
     ],
-    "CertDualVerificationTrial": [
-        {
-            "platforms": [
-                "mac"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "CertDualVerificationTrial"
-                    ]
-                }
-            ]
-        }
-    ],
     "CertVerifierBuiltin": [
         {
             "platforms": [