Remove homepage and redirect to /

- Removed relevent tests for homepage
- Updated tests which assumed homepage existed and used
  how-government-works instead. It is a simple page which should always
  work.
- Redirect /government to /
- Remove css and html for old homepage
Update unpublishing step to match data inputted
Merge pull request #668 from alphagov/remove-homepage

Remove homepage and redirect to /

https://www.pivotaltracker.com/story/show/52443665