buffer: remove unneeded eslint-disable comment

lib/buffer.js uses a function declaration for `Buffer`. So it never
uses an instance of `Buffer` in the global scope. Therefore the
disabling of the `require-buffer` custom rule is not needed. Remove the
comment.

PR-URL: nodejs/node#11906
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>

lib/buffer.js

@@ -1,4 +1,3 @@
-/* eslint-disable require-buffer */
 'use strict';
 
 const binding = process.binding('buffer');