Removing add_image_size

r_image_size.php

function add_new_thumbnails() {
    add_theme_support( 'post-thumbnails' );
   
    set_post_thumbnail_size( 56, 56, true ); // Normal post thumbnails
    add_image_size( 'tinyfeatured', 50, 50, true ); // Tiny Featured thumbnail
    add_image_size( 'blogonecol', 530, '', true ); // Blog One Column thumbnail
    add_image_size( 'post', 530, '', true ); // Portfolio Large thumbnail
    add_image_size( 'postnc', 700, '', false ); // Portfolio Large thumbnail
    add_image_size( 'carousel', 560, 341, true ); // Portfolio Large thumbnail
    add_image_size( 'magazine-full', '', 1131, true); // Portfolio Large thumbnail
  }

  add_action('init', 'add_new_thumbnails',10); //10 is default
 
if ( is_singular('issues') ) {
    function remove_thumbnails() {
        add_image_size( 'tinyfeatured', 0, 0 ); // Tiny Featured thumbnail
        add_image_size( 'blogonecol', 0, 0); // Blog One Column thumbnail
        add_image_size( 'post', 0,0 ); // Portfolio Large thumbnail
        add_image_size( 'postnc',0,0 ); // Portfolio Large thumbnail
        add_image_size( 'carousel',0,0 ); // Portfolio Large thumbnail
        add_image_size( 'magazine-full',0,0); // Portfolio Large thumbnail
    }
    add_action('init', 'remove_thumbnails',12); // 12 executes after 10

}