The leak detector is dead, long live asan and valgrind.

In resent times asan and valgrind have found way more memory management bugs
in llvm than the special purpose leak detector.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224703 91177308-0d34-0410-b5e6-96231b3b80d8