remove alternate queue implementation

the cited issues with stdlib Queue (and RLock which might be used to
re-implement Queue) is that it's not signal-safe.  Signal handling is
not the issue that twisted.threads is intended to address with
twisted.python.threadpool.  So this is out of scope.  Also, this might
not actually be a significant issue, because the only thing anyone
should ever call in a Twisted application in a signal handler is
`callFromThread` (which will talk to a pipe), not `callInThread` (which
talks to a queue).

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/branches/desynchronize-2673@43256 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb