This is a general cleanup after removing LockingMode related code.
It includes:
- Removing asserts() that are no longer necessary, since we removed legacy locking and monitor locking.
- Rewriting or deleting comments and arguments that are related to displaced headers.
- Dropping the lightweight prefix/suffix (e.g. fast_lock_lightweight and fast_unlock_lockweight should be renamed fast_lock and fast_unlock).
- Etc., etc.