Remove old darwin 12 LNT tester

Even though the compiler is good enough to suport C++11, the C++
standard library is unfortunately not.

As we have a new LNT -O3 tester at
http://lab.llvm.org:8011/builders/polly-perf-O3
we just remove the old tester.

This makes one constantly failing buildbot disappear.

git-svn-id: https://llvm.org/svn/llvm-project/zorg/trunk@200912 91177308-0d34-0410-b5e6-96231b3b80d8