Revert "[Lookalikes] Enable target embedding by default on ToT."

This reverts commit a6c2104c. It also
adds iOS to the list of impacted platforms.

Reason for revert: crbug.com/1152130

Original change's description:
> [Lookalikes] Enable target embedding by default on ToT.
>
> Bug: 1076617
> Change-Id: I5d818d4db60fad9e4cdc8e862d82a5bff6372560
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2505583
> Auto-Submit: Joe DeBlasio <jdeblasio@chromium.org>
> Commit-Queue: Steven Holte <holte@chromium.org>
> Reviewed-by: Steven Holte <holte@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#821978}

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

Bug: 1076617
Change-Id: I43c31dc635ae879aa3ad3a326ea48cf49751f735
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2555466
Auto-Submit: Joe DeBlasio <jdeblasio@chromium.org>
Reviewed-by: Livvie Lin <livvielin@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Joe DeBlasio <jdeblasio@chromium.org>
Commit-Queue: Joe DeBlasio <jdeblasio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832136}

components/lookalikes/core/features.cc

@@ -8,7 +8,7 @@ namespace lookalikes {
 namespace features {
 
 const base::Feature kDetectTargetEmbeddingLookalikes{
-    "TargetEmbeddingLookalikes", base::FEATURE_ENABLED_BY_DEFAULT};
+    "TargetEmbeddingLookalikes", base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kLookalikeInterstitialForPunycode{
     "LookalikeInterstitialForPunycode", base::FEATURE_ENABLED_BY_DEFAULT};

testing/variations/fieldtrial_testing_config.json

@@ -4119,6 +4119,26 @@
             ]
         }
     ],
+    "LookalikeTargetEmbeddingHeuristic": [
+        {
+            "platforms": [
+                "android",
+                "chromeos",
+                "ios",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "TargetEmbeddingLookalikes"
+                    ]
+                }
+            ]
+        }
+    ],
     "LowPriorityAdProcesses": [
         {
             "platforms": [