code: function(imageIdentifier, callback) {
          var url = this.getImageUrl(imageIdentifier, { usePrimaryHost: true }),
              signedUrl = this.getSignedResourceUrl('DELETE', url);
  
          request.del(signedUrl, callback);
          return this;
      }
docs: Delete an image
  
  @param {String}   imageIdentifier
  @param {Function} callback
  @return {ImboClient}