How to remove GrowlMail (on Mavericks)?

I've installed Mavericks and started to us the Mail app from Apple again, but every time I start Mail I get the message: > **Incompatible Plug-ins Disabled** > Mail has disabled the following plug-ins: > >Growlmail I've tried disabling and removing it in the System Preferences under Growl but the message above keeps popping up when I start Mail. How can I remove it?