Revert "[lit] Clean output directories before running tests."

This reverts commit da6318a92fba793e4f2447ec478b001392d57d43.

This is causing failures on some build bots due to what appears
to be some kind of lit ordering dependency.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306833 91177308-0d34-0410-b5e6-96231b3b80d8
15 files changed