Fix deletion of Array elements

Node-IRC uses `delete` keyword to remove things from Array which actually sets it to `undefined`. This causes unexpected errors like:

```
/home/ubuntu/scrollback/node_modules/irc/lib/irc.js:637
                    throw err;
                          ^
TypeError: Cannot call method 'replace' of undefined
    at /home/ubuntu/scrollback/node_modules/irc/lib/irc.js:239:71
    at Array.forEach (native)
    at Client.<anonymous> (/home/ubuntu/scrollback/node_modules/irc/lib/irc.js:226:26)
    at Client.EventEmitter.emit (events.js:95:17)
    at /home/ubuntu/scrollback/node_modules/irc/lib/irc.js:634:22
    at Array.forEach (native)
    at Socket.<anonymous> (/home/ubuntu/scrollback/node_modules/irc/lib/irc.js:631:15)
    at Socket.EventEmitter.emit (events.js:95:17)
    at Socket.<anonymous> (_stream_readable.js:720:14)
    at Socket.EventEmitter.emit (events.js:92:17)
```

This patch fixes this problem.