As far as I can tell, deleting a team project in TFS 2010 is still a task that must be completed at the VS2010 command line; while the operation is relatively straightforward, this command changes slightly with the introduction of project collections in TFS2010 and the value expected by /collection:<url> parameter may not be glaringly obvious.
Firstly, see the documentation.
Next, determine the URL for the team project you want to delete. I wasn't sure how to discover this but after some trial and error I found this format seems to work:
I've since realised the URL can be determined from the TFS Administration Console (in the General tab under the Team Project Collections node) and other derivatives returned a 404 error.
Note http://server:port/tfs is the Server URL configured for my TFS instance in the Administration Console so your mileage may vary.