Google fonts and loading speed

Hi,
I’m trying to speed up my site as much as possible.

I can see google fonts loading from the Pingdom and GT metrix waterfall report. It appears that google fonts are used in GDFModern?

This is in the functions.php anyway:

 // ENQUEUE GOOGLE FONTS
    add_action('wp_enqueue_scripts', 'gdfmodern_google_fonts');
    function gdfmodern_google_fonts()
    {

        wp_enqueue_style('google-fonts', '//fonts.googleapis.com/css?family=Lato:300,700|Roboto:700,300,400', array(), CHILD_THEME_VERSION);

    }

}

How can I remove Google fonts from the theme and presumably replace with websafe fonts? I have not picked Google fonts from GDF Options in the dashboard so I am not quite sure where they are loaded from.

Help with fonts that can speed up the site and limit external calls will be appreciated.

Thanks,
Lise