net: remove unused `var self = this` from old code

Removed an unused `var self = this` that is no longer required.

PR-URL: https://github.com/nodejs/node/pull/5224
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

lib/net.js

@@ -277,9 +277,8 @@ function writeAfterFIN(chunk, encoding, cb) {
 
   var er = new Error('This socket has been ended by the other party');
   er.code = 'EPIPE';
-  var self = this;
   // TODO: defer error events consistently everywhere, not just the cb
-  self.emit('error', er);
+  this.emit('error', er);
   if (typeof cb === 'function') {
     process.nextTick(cb, er);
   }