ZODB Components: Remove broken Subversion threading.RLock().

* This didn't work anyway with concurrent processes using the same SVN working
  copy (which is a frequent use case nowadays).
* Now that it has been migrated to ZODB Components, this also breaks on reset:
  1) Thread T1 acquires the lock.
  2) Thread T2 performs a reset.
  3) Thread T2 loads Subversion and thus a new RLock instance is created.
  => T2 can acquire the lock.