refactor: remove deprecation of supabasePersistSessionKey

Author: Vinzent03

packages/supabase_flutter/lib/src/local_storage.dart

@@ -8,7 +8,7 @@ import 'package:supabase_flutter/supabase_flutter.dart';
 import './local_storage_stub.dart'
     if (dart.library.html) './local_storage_web.dart' as web;
 
-@Deprecated("No longer in use")
+/// Only used for migration from Hive to SharedPreferences. Not actually in use.
 const supabasePersistSessionKey = 'SUPABASE_PERSIST_SESSION_KEY';
 
 /// LocalStorage is used to persist the user session in the device.