Update fieldtrial_testing_config to spec that Duet is disabled

The current set of experiments are not slated for launch, this patch
updates the field trial config to match that expectation.

Change-Id: I0299edbcc9cc38f49e55f725c31c67dbdf4ef951
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2057153
Auto-Submit: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742768}

testing/variations/fieldtrial_testing_config.json

@@ -1363,6 +1363,21 @@
             ]
         }
     ],
+    "ChromeDuet": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Disabled",
+                    "disable_features": [
+                        "ChromeDuet"
+                    ]
+                }
+            ]
+        }
+    ],
     "ChromeOSAssistantDspHotword": [
         {
             "platforms": [