Remove unused System Extensions code from Chromium

System Extensions's code is not used and has been slated for deletion.
This CL removes all references to system extensions code from Chromium.

BUG=1514407
TEST=Tryjobs

Change-Id: I4325e790cef770b07e043443f5a612d81f43e993
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5151201
Auto-Submit: Andrea Orru <[email protected]>
Commit-Queue: Andrea Orru <[email protected]>
Reviewed-by: Marc Treib <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1246366}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 9e6281d6..84a55b9 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -955,6 +955,11 @@
 // Deprecated 01/2024.
 const char kDownloadBubbleIphSuppression[] = "suppress_download_bubble_iph";
 
+#if BUILDFLAG(IS_CHROMEOS_ASH)
+// Deprecated 01/2024.
+const char kPersistedSystemExtensions[] = "system_extensions.persisted";
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
+
 // Register local state used only for migration (clearing or moving to a new
 // key).
 void RegisterLocalStatePrefsForMigration(PrefRegistrySimple* registry) {
@@ -1344,6 +1349,11 @@
 
   // Deprecated 01/2024.
   registry->RegisterBooleanPref(kDownloadBubbleIphSuppression, false);
+
+  // Deprecated 01/2024.
+#if BUILDFLAG(IS_CHROMEOS_ASH)
+  registry->RegisterDictionaryPref(kPersistedSystemExtensions);
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
 }
 
 void ClearSyncRequestedPrefAndMaybeMigrate(PrefService* profile_prefs) {
@@ -2572,6 +2582,11 @@
   // Added 01/2024.
   profile_prefs->ClearPref(kDownloadBubbleIphSuppression);
 
+#if BUILDFLAG(IS_CHROMEOS_ASH)
+  // Deprecated 01/2024.
+  profile_prefs->ClearPref(kPersistedSystemExtensions);
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
+
   // Please don't delete the following line. It is used by PRESUBMIT.py.
   // END_MIGRATE_OBSOLETE_PROFILE_PREFS