Remove nested listener locks

[natsukagami]

Upon discussions with @m8nmueller, we discovered that race does not necessarily require nested locking of
listeners (which is the only usage of the nested locks).
Instead the race implementation can just re-use the upsteam listener's lock and provide one if not yet existed.

With this out, I think we can just remove all the nested locking mechanisms. Should a legitimate need is raised
again in the future, we know that there is a sound and performant design ready.

Progress:

• Make race utilize existing upstream lock if possible
• Remove nested locks
• Rename lockCompletely -> acquireLock, lockSelf -> acquire