If you simply comment those two lines out, it will not add the "tbl-error" class to your form fields. Just remember, there is then no notification to the user of any error. I'm guessing that you're replacing the system with some customized version..
I guess it depends on the scenario. The login password should error when incorrect. Also, optionally you can change your password. However these fields must match. This is the purpose of the highlighting of those fields.