Revert "Clean up the AndroidSetupSearchEngine feature flag"

This reverts commit 4143ca0e9a31493152826915e8ed597429086e08.

Reason for revert: complication error at chrome internal

Original change's description:
> Clean up the AndroidSetupSearchEngine feature flag
> 
> The AndroidSetupSearchEngine feature is enabled by default
> and the config has no effect anymore.
> Therefore, remove the config and every reference to
> AndroidSetupSearchEngine.
> 
> Bug: 1057939
> Change-Id: I5e395d7ed031d93b64d4ae9d012f72351b0dec22
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2102032
> Reviewed-by: Friedrich [CET] <[email protected]>
> Reviewed-by: Scott Violet <[email protected]>
> Commit-Queue: Hwanseung Lee <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#750834}

[email protected],[email protected],[email protected]

Change-Id: I564011f94406cd750d9156b348fc04208e4530cf
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1057939
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2107336
Reviewed-by: Hwanseung Lee <[email protected]>
Commit-Queue: Hwanseung Lee <[email protected]>
Cr-Commit-Position: refs/heads/master@{#750929}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 5a3f7fb59..b80aaee 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1253,6 +1253,9 @@
 extern const char kAndroidAutofillAccessibilityName[];
 extern const char kAndroidAutofillAccessibilityDescription[];
 
+extern const char kAndroidSetupSearchEngineName[];
+extern const char kAndroidSetupSearchEngineDescription[];
+
 extern const char kAppNotificationStatusMessagingName[];
 extern const char kAppNotificationStatusMessagingDescription[];