Revert "Enable decode swap chain feature on waterfall"

This reverts commit e1f01a15.

Reason for revert: Makes video pixel tests flaky: crbug.com/917399

Original change's description:
> Enable decode swap chain feature on waterfall
> 
> Enables DirectCompositionUseNV12DecodeSwapChain and D3D11VideoDecoder
> features on waterfall.
> 
> Bug: 848093
> Change-Id: I561f5910a32cbe2adb1c47bd9c35df355bdce1a4
> Reviewed-on: https://chromium-review.googlesource.com/c/1364341
> Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
> Reviewed-by: Ilya Sherman <isherman@chromium.org>
> Reviewed-by: Frank Liberato <liberato@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#618447}

TBR=isherman@chromium.org,sunnyps@chromium.org,liberato@chromium.org

Change-Id: I13cb41b59140475eb46e789e8c94fc4e610ab614
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 848093, 917399
Reviewed-on: https://chromium-review.googlesource.com/c/1388645Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618549}

testing/variations/fieldtrial_testing_config.json

@@ -1342,36 +1342,6 @@
             ]
         }
     ],
-    "D3D11VP9Decoder": [
-        {
-            "platforms": [
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "D3D11VP9Decoder"
-                    ]
-                }
-            ]
-        }
-    ],
-    "D3D11VideoDecoder": [
-        {
-            "platforms": [
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "D3D11VideoDecoder"
-                    ]
-                }
-            ]
-        }
-    ],
     "DataCompressionProxyLoFi": [
         {
             "platforms": [
@@ -1604,21 +1574,6 @@
             ]
         }
     ],
-    "DirectCompositionUseNV12DecodeSwapChain": [
-        {
-            "platforms": [
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "DirectCompositionUseNV12DecodeSwapChain"
-                    ]
-                }
-            ]
-        }
-    ],
     "DownloadHomeMoreButton": [
         {
             "platforms": [