code: function(imageIdentifier, shortUrl, callback) {
          var id = shortUrl instanceof ShortUrl ? shortUrl.getId() : shortUrl,
              url = this.getImageUrl(imageIdentifier).setPath('/shorturls/' + id),
              signed = this.getSignedResourceUrl('DELETE', url);
  
          request.del(signed, callback);
          return this;
      }
docs: Delete a ShortUrl for a given imageIdentifier
  
  @param {String}               imageIdentifier
  @param {String|Imbo.ShortUrl} shortUrl
  @param {Function}             callback
  @return {ImboClient}