Revert "[Autofill] Add Autofill StrikeSystem to waterfall testing config"

This reverts commit e1a5c58c.

Reason for revert: Multiple reports of flakiness, see bugs.

Original change's description:
> [Autofill] Add Autofill StrikeSystem to waterfall testing config
> 
> Bug: 884817
> Change-Id: Iab61ac0b51d4541313f48263cadbfe2110fac543
> Reviewed-on: https://chromium-review.googlesource.com/c/1321255
> Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
> Commit-Queue: Jared Saul <jsaul@google.com>
> Cr-Commit-Position: refs/heads/master@{#606087}

TBR=rkaplow@chromium.org,jsaul@google.com

Change-Id: I6b8f3f6961891fc876900a574d2e3683fc63d5c0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 884817, 903055, 903080, 903083, 903228
Reviewed-on: https://chromium-review.googlesource.com/c/1326503Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606466}

testing/variations/fieldtrial_testing_config.json

@@ -752,25 +752,6 @@
             ]
         }
     ],
-    "AutofillSaveCreditCardUsesStrikeSystem": [
-        {
-            "platforms": [
-                "android",
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "AutofillSaveCreditCardUsesStrikeSystem"
-                    ]
-                }
-            ]
-        }
-    ],
     "AutofillSingleClick": [
         {
             "platforms": [