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.

llvm-svn: 257268