Update client testing config to match server group

Bug: 967960
Change-Id: I29fd49d9c4a1a38a686e50a7dac58481c64e5938
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2303996Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789324}

testing/variations/fieldtrial_testing_config.json

@@ -4769,7 +4769,7 @@
             ]
         }
     ],
-    "OmniboxSearchEngineLogo": [
+    "OmniboxSearchEngineLogoAndroid": [
         {
             "platforms": [
                 "android"