Cleanup: Delete os_sync_util::MigrateOsSyncPreferences()

This migration has been running for about a year, so it can be cleaned
up now.

OBSOLETE_HISTOGRAM[ChromeOS.Sync.PreferencesMigrated]=Migration completed as of 2023-06.

Bug: 1249845
Change-Id: If083895da7f63f6266e824bea2f0bccf357e509e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4604314
Reviewed-by: James Cook <[email protected]>
Commit-Queue: Marc Treib <[email protected]>
Reviewed-by: Jorge Lucangeli Obes <[email protected]>
Reviewed-by: Mikel Astiz <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1157407}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 6adbc42..f5d371f0c 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -883,6 +883,11 @@
 // Deprecated 06/2023.
 const char kWebAppsExtensionIDs[] = "web_apps.extension_ids";
 
+// Deprecated 06/2023.
+#if BUILDFLAG(IS_CHROMEOS_ASH)
+constexpr char kOsSyncPrefsMigrated[] = "sync.os_sync_prefs_migrated";
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
+
 // Register local state used only for migration (clearing or moving to a new
 // key).
 void RegisterLocalStatePrefsForMigration(PrefRegistrySimple* registry) {
@@ -1255,6 +1260,11 @@
 
   // Deprecated 06/2023.
   registry->RegisterDictionaryPref(kWebAppsExtensionIDs);
+
+  // Deprecated 06/2023.
+#if BUILDFLAG(IS_CHROMEOS_ASH)
+  registry->RegisterBooleanPref(kOsSyncPrefsMigrated, false);
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
 }
 
 }  // namespace
@@ -2360,6 +2370,11 @@
   // Added 06/2023.
   profile_prefs->ClearPref(kWebAppsExtensionIDs);
 
+  // Added 06/2023.
+#if BUILDFLAG(IS_CHROMEOS_ASH)
+  profile_prefs->ClearPref(kOsSyncPrefsMigrated);
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
+
   // Please don't delete the following line. It is used by PRESUBMIT.py.
   // END_MIGRATE_OBSOLETE_PROFILE_PREFS