Update fieldtrial_testing_config for new CSD model

Client Side Detection models are based on a combination of a DOM model
and a vision-based model. The most recent DOM model was found to be
faulty, so we need to rollout new combined models. This CL updates
the fieldtrial_testing_config to be in sync with the config changes.

Change-Id: Id50dc55a52c927567dd97d76715098fd7c53de6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437007
Auto-Submit: Daniel Rubery <drubery@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812265}

testing/variations/fieldtrial_testing_config.json

@@ -1584,9 +1584,9 @@
             ],
             "experiments": [
                 {
-                    "name": "EnabledWithVisualModel",
+                    "name": "EnabledWithVisualModel2",
                     "params": {
-                        "ModelNum": "5"
+                        "ModelNum": "6"
                     },
                     "enable_features": [
                         "ClientSideDetectionModel"