remove explicit require to buffer

A variable `Buffer` is provided by the module system, so this is not
required.

Author: sokra

helpers.js

@@ -1,4 +1,3 @@
-var Buffer = require('buffer').Buffer;
 var intSize = 4;
 var zeroBuffer = new Buffer(intSize); zeroBuffer.fill(0);
 var chrsz = 8;

index.js

@@ -1,4 +1,3 @@
-var Buffer = require('buffer').Buffer
 var rng = require('./rng')
 
 function error () {

pbkdf2.js

@@ -3,8 +3,6 @@
 // Licensed under LGPL v3
 // Copyright (c) 2013 jduncanator
 
-var Buffer = require('buffer').Buffer
-
 var blocksize = 64
 var zeroBuffer = new Buffer(blocksize); zeroBuffer.fill(0)