Josh created a custom index.php way back in WordPress 1.5 days that removed the RSS feeds on the WordPress dashboard.
Up until now it wasn't really possible to this with a plugin nicely. WordPress 2.2 has added an API hook that although not relevant to the Dashboard it is in the right place!
So I've created a simple plugin, which you can download here, that removes the RSS feeds. Please note it requires WordPress 2.2.