$('.cf-table-add-row').hide(); should work. If not, something else might be going wrong in the code in which case I'd suggest looking for any JavaScript errors in the console.

However, if there's a chance you might have more than one table you should include the table class.

The problem with your second option is that you have the two classes together in the selector (no space) meaning it is looking for something with both of those classes.

You should have a space between them so it looks for something with the add row class within something with the GLTable class.

$('.GLTable .cf-table-add-row').hide();

You should be able to test these in the browser console to make sure they do what you want before you start modifying the form's JavaScript.