The default WordPress administration menu uses the names of the PHP code files used to render each section as their unique identifiers. One way to quickly find out the identifier for a menu item is to hover the mouse cursor over it in a web browser and to look at the address that the link points to. In the case of the Comments menu item, the URL is http://localhost/wp-admin/edit-comments.php ; thus the use of edit-comments.php in the call to remove_menu_page.
A similar technique was used to determine the arguments to pass to the remove_submenu_page function, identifying that the Settings section has a URL of http://localhost/wp-admin/options-general.php , while the Permalinks section has the address http://localhost/wp-admin/options-permalink.php.