Redmine

The best way to get rid of the menu is to delete its entries in a custom plugin.

You can remove the menu items in your plugins init.rb file like this:

delete_menu_item :application_menu, :calendar

You can find the menu items in source:trunk/lib/redmine.rb#L203.

I started something similar a few days ago in a different plugin.
Maybe you can checkout my plugin and use it as boilerplate.