test: fix lint error regarding unused commons const

Currently, make lint is failing with the following error:
3:7  error  'common' is assigned a value but never used  no-unused-vars
✖ 1 problem (1 error, 0 warnings)

PR-URL: nodejs#9334
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

test/parallel/test-stream-writableState-ending.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const common = require('../common');
+require('../common');
 
 const assert = require('assert');
 const stream = require('stream');