Revert "Enable...

Revert "Enable StopHookForMultipleThreadsTestCase::test_stop_hook_multiple_threads_with_dwarf on FreeBSD"

And update the comment describing the reason this test is skipped.
Unlike the issue described llvm.org/pr22784 this test sometimes causes
a hang on my local machine and is not just a problem on the retired
buildbot.

This reverts commit r247013.

llvm-svn: 247024