Fix GreenDragon bots

This commit removes a very old deprecated API that was causing compile failures for LLDB on Darwin. Since the comment says we only needed to keep the old API around for a few Xcode builds, and the comment was written 6 years ago... I think this can safely go away.

Failure URL:
http://lab.llvm.org:8080/green/view/LLDB/job/lldb_build_test/29936/console

llvm-svn: 308509