Wordpress - Remove Categories / Tags From Admin Menu

add_action('admin_menu', 'my_remove_sub_menus');

function my_remove_sub_menus() {
    remove_submenu_page('edit.php', 'edit-tags.php?taxonomy=category');
    remove_submenu_page('edit.php', 'edit-tags.php?taxonomy=post_tag');
}

If you want to completely remove categories and tags you can do so like this:

// Remove Categories and Tags
add_action('init', 'myprefix_remove_tax');
function myprefix_remove_tax() {
    register_taxonomy('category', array());
    register_taxonomy('post_tag', array());
}

You may also want to remove the meta boxes from the Post Creation page

// REMOVE POST META BOXES
function remove_my_post_metaboxes() {
  remove_meta_box( 'categorydiv','post','normal' ); // Categories Metabox
  remove_meta_box( 'tagsdiv-post_tag','post','normal' ); // Tags Metabox
}
add_action('admin_menu','remove_my_post_metaboxes');