Remove DialMediaRouteProvider from testing config.

Bug: 1126640, 1024661
Change-Id: I1243ce07f422d95b85df81bc68962c1443868f7a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500702Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Cr-Commit-Position: refs/heads/master@{#821173}

testing/variations/fieldtrial_testing_config.json

@@ -2303,24 +2303,6 @@
             ]
         }
     ],
-    "DialMediaRouteProvider": [
-        {
-            "platforms": [
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "DialMediaRouteProvider"
-                    ]
-                }
-            ]
-        }
-    ],
     "DirectActions": [
         {
             "platforms": [