Under Options --> Mame --> Basic --> Command line (at the bottom), you need to add -skip_gameinfo somehow, though I'm not sure how the syntax works, as I can't get it to work either.
Others may know, but you could just edit mame.ini directly. Open your Mame folder and edit your mame.ini file. Scroll all the way down until you see the "core misc options" section. Set skip_gameinfo to 1 instead of 0. Save the file.