Remove require('buffer') in built-in libraries.

lib/dgram.js

@@ -3,7 +3,6 @@ var fs = require("fs");
 var events = require("events");
 var dns = require('dns');
 
-var Buffer = require('buffer').Buffer;
 var IOWatcher    = process.binding('io_watcher').IOWatcher;
 var binding      = process.binding('net');
 var socket       = binding.socket;

lib/fs.js

@@ -1,6 +1,5 @@
 var sys = require('sys');
 var events = require('events');
-var Buffer = require('buffer').Buffer;
 
 var binding = process.binding('fs');
 var constants = process.binding('constants');

lib/http.js

@@ -10,7 +10,6 @@ if (debugLevel & 0x4) {
 
 var net = require('net');
 var events = require('events');
-var Buffer = require('buffer').Buffer;
 
 var FreeList = require('freelist').FreeList;
 var HTTPParser = process.binding('http_parser').HTTPParser;

lib/net.js

@@ -20,7 +20,6 @@ var binding = process.binding('net');
 // represent buffer.used) that can be seeked around would be easier. I'm not
 // yet convinced that every use-case can be fit into that abstraction, so
 // waiting to implement it until I get more experience with this.
-var Buffer = require('buffer').Buffer;
 var FreeList = require('freelist').FreeList;
 
 var IOWatcher   = process.binding('io_watcher').IOWatcher;

lib/readline.js

@@ -7,8 +7,6 @@
 var kHistorySize = 30;
 var kBufSize = 10*1024;
 
-
-var Buffer = require('buffer').Buffer;
 var sys = require('sys');
 var inherits = require('sys').inherits;
 var EventEmitter = require('events').EventEmitter;

lib/string_decoder.js

@@ -1,5 +1,3 @@
-var Buffer = require('buffer').Buffer;
-
 var StringDecoder = exports.StringDecoder = function (encoding) {
   this.encoding = (encoding || 'utf8').toLowerCase().replace(/[-_]/,'');
   if (this.encoding === 'utf8') {