Remove IOSurfaceCapturer from field trial config

IOSurfaceCapturer has been enabled 100% everywhere. So remove the
related field trial testing config.

Bug: 840597
Change-Id: I3d79b5f734c86ec5197527e7c7736c0233dcff71
Reviewed-on: https://chromium-review.googlesource.com/1185526Reviewed-by: Robert Kaplow (slow) <rkaplow@chromium.org>
Commit-Queue: Weiyong Yao <braveyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585518}

testing/variations/fieldtrial_testing_config.json

@@ -1948,21 +1948,6 @@
             ]
         }
     ],
-    "IOSurfaceCapturer": [
-        {
-            "platforms": [
-                "mac"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "IOSurfaceCapturer"
-                    ]
-                }
-            ]
-        }
-    ],
     "ImprovedRecoveryComponent": [
         {
             "platforms": [