Remove obsolete fieldtrial_testing_config keys for experiments that were defaulted or abandoned.

Bug: 951299
Change-Id: I5b27fa435bd8c81c1e3a76967a870ee3495f5ad8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1762080
Auto-Submit: Konrad Hofbauer <hofbauer@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688542}

testing/variations/fieldtrial_testing_config.json

@@ -6676,23 +6676,6 @@
             ]
         }
     ],
-    "WebRTC-Audio-NetEqPostponeDecodingAfterExpand": [
-        {
-            "platforms": [
-                "windows",
-                "mac",
-                "chromeos",
-                "linux",
-                "ios",
-                "android_webview"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled"
-                }
-            ]
-        }
-    ],
     "WebRTC-Audio-NewOpusPacketLossRateOptimization": [
         {
             "platforms": [
@@ -6726,24 +6709,6 @@
             ]
         }
     ],
-    "WebRTC-Bwe-LossBasedControl": [
-        {
-            "platforms": [
-                "windows",
-                "mac",
-                "chromeos",
-                "linux",
-                "ios",
-                "android",
-                "android_webview"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled,balance_incr:5kbps,balance_decr:24kbps,exponent:0.7,resets:true"
-                }
-            ]
-        }
-    ],
     "WebRTC-Bwe-MaxRttLimit": [
         {
             "platforms": [
@@ -6762,23 +6727,6 @@
             ]
         }
     ],
-    "WebRTC-BweAllocProbingOnlyInAlr": [
-        {
-            "platforms": [
-                "windows",
-                "mac",
-                "chromeos",
-                "linux",
-                "ios",
-                "android"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled"
-                }
-            ]
-        }
-    ],
     "WebRTC-CongestionWindow": [
         {
             "platforms": [
@@ -6852,24 +6800,6 @@
             ]
         }
     ],
-    "WebRTC-KeepAbsSendTimeExtension": [
-        {
-            "platforms": [
-                "windows",
-                "mac",
-                "chromeos",
-                "linux",
-                "ios",
-                "android",
-                "android_webview"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled"
-                }
-            ]
-        }
-    ],
     "WebRTC-LocalIPPermissionCheck": [
         {
             "platforms": [