Do not run dead-code-elimination on polly-detect bot

The polly detect should just track the performance of our scop detection
phase. Dead code elimination is not part of this phase. When it was
added we forgot to disable it on this builder.

git-svn-id: https://llvm.org/svn/llvm-project/zorg/trunk@210653 91177308-0d34-0410-b5e6-96231b3b80d8