[SmartLock] Delete Sign in with Smart Lock removed notification

Enough time has elapsed to notify users about changes to Smart Lock.
We can delete the code for this notification. I've deleted the
kHasSeenSmartLockSignInRemovedNotification pref according to
documentation in chrome/browser/prefs/README.md.

TEST=existing unittests pass and manually tested smart lock with
strongbad and pixel4a

Change-Id: If22dcdffd598829f0dc92d023c0b63e1a090b82d
Bug: b/227674947
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4278762
Reviewed-by: David Trainor <[email protected]>
Reviewed-by: Denis Kuznetsov <[email protected]>
Commit-Queue: Brittany Hartmire <[email protected]>
Reviewed-by: Will Harris <[email protected]>
Reviewed-by: Ryan Hansberry <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1109870}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index ff57c231..9dbc2e5 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -794,6 +794,12 @@
 const char kWebAppsUrlHandlerInfo[] = "web_apps.url_handler_info";
 #endif  // BUILDFLAG(IS_WIN) || BUILDFLAG(IS_MAC) || BUILDFLAG(IS_LINUX)
 
+// Deprecated 02/2023.
+#if BUILDFLAG(IS_CHROMEOS_ASH)
+const char kHasSeenSmartLockSignInRemovedNotification[] =
+    "easy_unlock.has_seen_smart_lock_sign_in_removed_notification";
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
+
 // Register local state used only for migration (clearing or moving to a new
 // key).
 void RegisterLocalStatePrefsForMigration(PrefRegistrySimple* registry) {
@@ -1061,6 +1067,12 @@
                                  base::FilePath());
   registry->RegisterListPref(kPluginsPluginsList);
   registry->RegisterBooleanPref(kPluginsShowDetails, false);
+
+// Deprecated 02/2023.
+#if BUILDFLAG(IS_CHROMEOS_ASH)
+  registry->RegisterBooleanPref(kHasSeenSmartLockSignInRemovedNotification,
+                                false);
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
 }
 
 }  // namespace
@@ -2089,6 +2101,11 @@
   profile_prefs->ClearPref(kPluginsPluginsList);
   profile_prefs->ClearPref(kPluginsShowDetails);
 
+// Added 02/2023.
+#if BUILDFLAG(IS_CHROMEOS_ASH)
+  profile_prefs->ClearPref(kHasSeenSmartLockSignInRemovedNotification);
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
+
   // Please don't delete the following line. It is used by PRESUBMIT.py.
   // END_MIGRATE_OBSOLETE_PROFILE_PREFS