The mode-line can be toggled on and off with the palindromic interactive command, mode-line-mode.
You can turn the mode-line on and off in your rc, too. Simply call the function mode_line_mode. If you pass no argument, it toggles the mode-line, as with the interactive command described earlier. If you pass true, it turns the mode line on, and if you pass false, it turns the mode line off. Since the mode-line is on by default, and most people who will come looking here will do so because they want to turn it off, here is the full code to turn off the mode-line in your rc.