Reduce number of tests for the 'View edition' button

The `should_link_to_public_version_when_published` and its counterpart,
`should_not_link_to_public_version_when_not_published` test macros were both
used in 10 controller tests. The two tests in those macros were exercising
logic in the editions/navigation partial which is shared by all those
controllers. By changing these tests to use the `GenericEditionsController` we
can reduce the number of functional tests by 18 (20 down to 2).