test: remove unused variables form http tests

The http tests seem especially prone to including unused variables.
This change removes them.

PR-URL: https://github.com/nodejs/node/pull/4422
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>

test/parallel/test-http-client-encoding.js

@@ -1,6 +1,5 @@
 'use strict';
 var common = require('../common');
-var assert = require('assert');
 
 var http = require('http');