Hi,
I think the information Justin gave only avoid Moodle to tell "Missing from disk!", this plugin no more "registered" in mdl_config_plugins.
And as he said as NB, for a real good deletion of a plugin, you should :
- have the plugin files installed in your Moodle, so you have the "Uninstall" link
- uninstall the plugin via the link
- then delete plugin files
HTH,
Séverin