Remove lldb's custom copy of the C++ demangler, used only on Mac
OS X.  Testsuite shows no change in results using the system runtime's
demangler.
<rdar://problem/12029914> 


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@185510 91177308-0d34-0410-b5e6-96231b3b80d8