remove trailer methods

less common than .auth which we removed as well but we can
add them back if it becomes a common request

lib/context.js

@@ -924,31 +924,6 @@ Context.prototype = {
     }
   },
 
-  /**
-   * Get the trailing headers to a request.
-   *
-   * @param {Object}
-   * @api public
-   */
-
-  get trailers() {
-    return this.req.trailers;
-  },
-
-  /**
-   * Add trailing headers to the response.
-   *
-   * Maybe:
-   *   - throw if not chunked encoding
-   *
-   * @param {object} headers
-   * @api public
-   */
-
-  addTrailers: function(headers){
-    return this.res.addTrailers(headers);
-  },
-
   /**
    * Append `val` to header `field`.
    *