The LockManager version can also use MySQL as backend, so there's hardly a point in maintaining the old locking along the LockManager version.
There are two default LockManagers in MediaWiki:
$wgLockManagers[] = [ 'name' => 'fsLockManager', 'class' => 'FSLockManager', 'lockDirectory' => "{$wgUploadDirectory}/lockdir", ]; $wgLockManagers[] = [ 'name' => 'nullLockManager', 'class' => 'NullLockManager', ];
I guess fsLockManager could be our new default.