Reduce number of tests for the 'view preview' button

The `should_link_to_preview_version_when_not_published` test macro was used in
10 controller tests. The single test in that macro was 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 9 (from 10 to 1).