<?php
function _s_silence_content_image_sizes_attr($size, $image_src)
{
    if (get_page_template_slug() === 'template-full_width.php') {
        //Do something here
    }
    
    if (!is_array($size) && $size == 'hero-image') {
        return false;
    }
}
add_filter('wp_calculate_image_sizes', '_s_silence_content_image_sizes_attr', 10 , 2);
?>