When playing around with custom Work Item Types, there will be a moment you want to delete this item. Standard this isn't possible.  But when you install the Microsoft Power Tools for TFS, you have a program tfpt.

With this program you could use the command destroywitd, which will delete your WIT. Use it this way:

tfpt destroywitd /server:<tfsservername> /project:<projectname> /workitemtype:<witdname>

The WIT will now be physically removed from the server and can't be resrtored.