Revert of r179378 and r179329, which introduce a private thread lock around thread enumeration,
in order to prevent consistent hangs on all 3 LLDB buildbots.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@179759 91177308-0d34-0410-b5e6-96231b3b80d8