Revert "[ntp][modules] Add shopping module fieldtrial_testing_config.json"

This reverts commit 0b7367ff10.

Reason for revert: A culprit CL which might break NTP tests
here:
https://ci.chromium.org/ui/p/chromium/builders/ci/Linux%20MSan%20Tests/26482/overview

Original change's description:
> [ntp][modules] Add shopping module fieldtrial_testing_config.json
>
> Bug: 1110075
> Change-Id: I735506c3e0efff1f92582498400bea0a914cf215
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2566374
> Auto-Submit: Tibor Goldschwendt <tiborg@chromium.org>
> Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
> Reviewed-by: Caitlin Fischer <caitlinfischer@google.com>
> Commit-Queue: Tibor Goldschwendt <tiborg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#833561}

TBR=mahmadi@chromium.org,tiborg@chromium.org,caitlinfischer@google.com,chromium-scoped@luci-project-accounts.iam.gserviceaccount.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1110075
Change-Id: I865c3885224e08eaf1abbd0a0afab690fe5f1449
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2576065
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834123}

testing/variations/fieldtrial_testing_config.json

@@ -2304,25 +2304,6 @@
             ]
         }
     ],
-    "DesktopNtpShoppingTasksModule": [
-        {
-            "platforms": [
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "NtpModules",
-                        "NtpShoppingTasksModule"
-                    ]
-                }
-            ]
-        }
-    ],
     "DesktopTabGroupsCollapse": [
         {
             "platforms": [