Remove "delay_tcp_race": "true" from QUIC testing variations since it is now on by default and not …

testing/variations/fieldtrial_testing_config_mac.json

 {
     "AutofillClassifier": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
@@ skipping 283 matching lines @@
     "PreconnectMore": [
         {
             "enable_features": [
                 "PreconnectMore"
             ],
             "group_name": "Enabled"
         }
     ],
     "QUIC": [
         {
-            "group_name": "Enabled",
-            "params": {
-                "delay_tcp_race": "true"
-            }
+            "group_name": "Enabled"
         }
     ],
     "RafAlignedInput": [
         {
             "enable_features": [
                 "RafAlignedInput"
             ],
             "group_name": "Enabled"
         }
     ],
@@ skipping 248 matching lines @@
     ],
     "use-new-media-cache": [
         {
             "enable_features": [
                 "use-new-media-cache"
             ],
             "group_name": "Enabled"
         }
     ]
 }