Changing testing param to a different experiment group

This is multi-arm experiment, but it should move to a single arm
experiment with parameter set to 60 seconds.

Change-Id: Ibbbac52e4f9583eb858bc8724364850afcfd94cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1554799
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#648675}

testing/variations/fieldtrial_testing_config.json

@@ -3014,9 +3014,9 @@
             ],
             "experiments": [
                 {
-                    "name": "Enabled_300_seconds_20190314",
+                    "name": "Enabled_60_seconds_20190408",
                     "params": {
-                        "unused_idle_socket_timeout_seconds": "300"
+                        "unused_idle_socket_timeout_seconds": "60"
                     },
                     "enable_features": [
                         "NetUnusedIdleSocketTimeout"