Remove child category from URL

You can use the post_link_category filter to remove child categories from permalinks:

function wpse147453_remove_child_categories_from_permalinks( $category ) {
    while ( $category->parent ) {
        $category = get_term( $category->parent, 'category' );
    }

    return $category;
}
add_filter( 'post_link_category', 'wpse147453_remove_child_categories_from_permalinks' );