bpo-39995: Split test_concurrent_futures.test_crash() into sub-tests (GH-19739)

Now only test_error_during_result_unpickle_in_result_handler()
captures and ignores sys.stderr in the test process.

Tools like test.bisect_cmd don't support subTest() but only
work with the granularity of one method.

Remove unused ExecutorDeadlockTest._sleep_id() method.