Remove `require(sys)` statement from `tst/ber/writer.test.js` because it is no longer supported or required

See: https://github.com/mcavage/node-asn1/pull/17

```
@@ -1,7 +1,6 @@
  // Copyright 2011 Mark Cavage <mcavage@gmail.com> All rights reserved.
  
  var test = require('tap').test;
 -var sys = require('sys');
  
  ///--- Globals
```