Revert "Add HTTP-Bad Phase 3 experiment to field trial testing config"

This reverts commit 1b6c18ab.

Reason for revert:
This broke two browser_tests in Official Windows builds:
SecurityStateTabHelperTest.DefaultSecurityLevelOnFilesystemUrl
SecurityStateTabHelperTest.DefaultSecurityLevelOnBlobUrl

Original change's description:
> Add HTTP-Bad Phase 3 experiment to field trial testing config
> 
> Some browser tests needed to be updated accordingly. I deleted a couple
> that were redundant with tests where the field trial is enabled. For a
> few others that only made sense in the pre-field trial world, I just
> disabled the feature for them, though we'll want to clean them up
> eventually after the field trial launches.
> 
> Bug: 807062
> Change-Id: I480b2527375368d6146c1ddace2551dece9ec596
> Reviewed-on: https://chromium-review.googlesource.com/891677
> Reviewed-by: Eric Lawrence <elawrence@chromium.org>
> Reviewed-by: Jesse Doherty <jwd@chromium.org>
> Commit-Queue: Emily Stark <estark@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#533845}

TBR=jwd@chromium.org,estark@chromium.org,elawrence@chromium.org

Change-Id: I34688c6ef005ac74e79d78a5b8d451790dba96a5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 807062, 808424
Reviewed-on: https://chromium-review.googlesource.com/899150Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534048}

testing/variations/fieldtrial_testing_config.json

@@ -1596,29 +1596,6 @@
             ]
         }
     ],
-    "HTTPBadPhase3": [
-        {
-            "platforms": [
-                "android",
-                "chromeos",
-                "ios",
-                "linux",
-                "mac",
-                "win"
-            ],
-            "experiments": [
-                {
-                    "name": "NotSecureWarning",
-                    "params": {
-                        "treatment": "warning"
-                    },
-                    "enable_features": [
-                        "MarkHttpAs"
-                    ]
-                }
-            ]
-        }
-    ],
     "Html5ByDefault": [
         {
             "platforms": [