thread/thread.c: no dup

* ext/thread/thread.c (Init_thread): ConditionVariable and Queue
  are not able to copy.  [ruby-core:59961] [Bug #9440]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44681 b2dd03c8-39d4-4d8f-98ff-823fe69b080e