'Unregisters the given plugin(s).
If a plugin isn\'t already registered, this will raise PluginNotRegistered.'

def unregister_plugin(self, plugin):

    plugin_name = plugin.__name__
    if (plugin_name not in self.plugins):
        raise PluginNotRegistered(('The    plugin    %r    is    not    registered' % plugin))
    del self.plugins[plugin_name]
