You can use add_filter( 'get_image_tag_class', '__return_empty_string' );
To remove all classes
You can also use
add_filter('get_image_tag_class','add_custom_image_class');
function add_custom_image_class($class){
$class .= ' news__img';
return $class;
}
To add new classes. This only works when adding images after the code is in place not to existing images.
Alternatively, you could look to use jQuery and do a find/replace on the class
