Deregister CSS style link ‘open-sans-css’

WP Core actually uses Open Sans font; it’s not a plugin. there is a plugin that removes it, but you can probably simply dequeue or deregister it.

adding this to functions.php should work; if you want it removed from the backend as well, hook into the admin_print_styles action.

function dequeue_opensans_css() {
    wp_dequeue_style( 'open-sans' );
}
add_action( 'wp_enqueue_scripts', 'dequeue_opensans_css', 999 );

if it’s in the footer, change the add_action() line:

add_action('wp_footer','dequeue _opensans_css',1);

untested, but that should work.