Revert "Teach the CMake build system to run lit's test suite. These can be run"

Revert "Teach the CMake build system to run lit's test suite. These can be run"

This reverts r257221.

This caused several build bot failures

* It looks like some of the tests don't work correctly under Windows
* It looks like the lit per test timeout tests fail

So I'm reverting for now. Once the above failures are fixed running
lit's tests can be enabled again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257268 91177308-0d34-0410-b5e6-96231b3b80d8