Remove field trial for VerifyHTMLFetchedFromAppCacheBeforeDelay

Due to performance regressions related to the field trial, it seems like
the best course of action is to (temporarily) remove it, so that it
won't impact stable. This CL removes the field trial configuration.

Bug: 1036347
Change-Id: I12fbd9e16137d8f5e5803d8502ce80e0b907cae1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2023497Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Yoav Weiss <yoavweiss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736854}

testing/variations/fieldtrial_testing_config.json

@@ -7128,26 +7128,6 @@
             ]
         }
     ],
-    "VerifyHTMLFetchedFromAppCacheBeforeDelay": [
-        {
-            "platforms": [
-                "windows",
-                "mac",
-                "chromeos",
-                "linux",
-                "ios",
-                "android"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "VerifyHTMLFetchedFromAppCacheBeforeDelay"
-                    ]
-                }
-            ]
-        }
-    ],
     "VideoCaptureService": [
         {
             "platforms": [