streams: remove unused require('assert')

Author: rvagg

lib/_stream_writable.js

@@ -27,7 +27,6 @@ module.exports = Writable;
 Writable.WritableState = WritableState;
 
 var util = require('util');
-var assert = require('assert');
 var Stream = require('stream');
 
 util.inherits(Writable, Stream);