Restoring field trial config for AudioService experiment on linux/mac

To make bots to run the audio service in a utility process,
launched on startup.
This will result in expected performance regressions in media tests
(see the bug).

Bug: 870171
Change-Id: Id301763a6117d0b4a4d26809d74032c4c188c1e2
Reviewed-on: https://chromium-review.googlesource.com/1199185Reviewed-by: Robert Kaplow (slow) <rkaplow@chromium.org>
Commit-Queue: Olga Sharonova <olka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588374}

testing/variations/fieldtrial_testing_config.json

@@ -443,6 +443,8 @@
     "AudioService": [
         {
             "platforms": [
+                "linux",
+                "mac",
                 "windows"
             ],
             "experiments": [
@@ -459,23 +461,6 @@
                 }
             ]
         },
-        {
-            "platforms": [
-                "linux",
-                "mac"
-            ],
-            "experiments": [
-                {
-                    "name": "AudioServiceStreams_v6",
-                    "params": {
-                        "teardown_timeout_s": "0"
-                    },
-                    "enable_features": [
-                        "AudioServiceAudioStreams"
-                    ]
-                }
-            ]
-        },
         {
             "platforms": [
                 "android",