Remove a useless test

Hi,

Two work tests (`testDeleteWork()` and `testDeleteWorkWithNoCopies()`) are testing the same thing: deleteWork. One of them loops over  `copies` populated by the `Work,getCopies()` method, but it returns nothing, so the loop never gets run.  The two tests are the same so we should remove one.

@JonathanShaw @scoen 

Huw