ZTS: Remove exceptions for flaky zhack on FreeBSD
Issue #11854 has been resolved, so we can remove the exceptions for it.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #12527