Revert "Create field trial for hover card images."

This reverts commit 9ba868cd.

Reason for revert: <INSERT REASONING HERE>
interactive_ui_tests failed on
Builder Linux TSan Tests
https://ci.chromium.org/p/chromium/builders/ci/Linux%20TSan%20Tests

Original change's description:
> Create field trial for hover card images.
> 
> This is required to deploy a finch configuration.
> See cr/296239960 for WIP Finch config.
> 
> Bug: 1032640
> Change-Id: Ifae3d2966d4ca908982cec37c5d88f786bf07367
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2067558
> Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
> Commit-Queue: Dana Fried <dfried@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#743826}

TBR=rkaplow@chromium.org,dfried@chromium.org

Change-Id: I27fbe4d67b42a42d63757e78427d86d31e045592
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1032640
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2069275Reviewed-by: Lan Wei <lanwei@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743839}

testing/variations/fieldtrial_testing_config.json

@@ -5948,24 +5948,6 @@
             ]
         }
     ],
-    "TabHoverCardImages": [
-        {
-            "platforms": [
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "TabHoverCardImages"
-                    ]
-                }
-            ]
-        }
-    ],
     "TabHoverCards": [
         {
             "platforms": [