Reduce number of tests for 'delete edition' button

The `should_be_able_to_delete_an_edition` test macro was used in 10 controller
tests. The tests in the macro were exercising logic in the editions/navigation
partial and the editions controller, all of which are shared across those 10
controllers. By changing these tests to use the generic editions controller we
can reduce the number of functional tests from 70 to 7.

*NOTE*. It should be possible to further simplify the tests for the
presence/absence of the delete button as the template only switches based on
the value of `Edition#deletable?` (i.e. it doesn't care about the actual state
of the edition).