repl: remove 'repl' from automatic loading libs

In repl, calling `repl` twice shows the following message:
```
> repl
A different "repl" already exists globally
```

lib/repl.js

@@ -70,7 +70,7 @@ exports.writer = util.inspect;
 
 exports._builtinLibs = ['assert', 'buffer', 'child_process', 'cluster',
   'crypto', 'dgram', 'dns', 'domain', 'events', 'fs', 'http', 'https', 'net',
-  'os', 'path', 'punycode', 'querystring', 'readline', 'repl', 'stream',
+  'os', 'path', 'punycode', 'querystring', 'readline', 'stream',
   'string_decoder', 'tls', 'tty', 'url', 'util', 'vm', 'zlib'];