Reduce navigation menu to one level depth in Genesis. Source: StudioPress Generate Pro child theme

reduce-primary-navigation-menu-one-level-depth.php

<?php

//* Reduce the primary navigation menu to one level depth
add_filter( 'wp_nav_menu_args', 'prefix_generate_primary_menu_args' );
function prefix_generate_primary_menu_args( $args ){

	if( 'primary' != $args['theme_location'] )
	return $args;

	$args['depth'] = 1;
	return $args;

}

reduce-secondary-navigation-menu-one-level-depth.php

<?php

//* Reduce the secondary navigation menu to one level depth
add_filter( 'wp_nav_menu_args', 'prefix_generate_secondary_menu_args' );
function prefix_generate_secondary_menu_args( $args ){

	if( 'secondary' != $args['theme_location'] )
	return $args;

	$args['depth'] = 1;
	return $args;

}