Before we disabled featured proposals by default, there were many tests
creating them because they were needed in order to create non-featured
proposals.
But now these tests don't need to create featured proposals anymore.
The `type: :feature` is automatically detected by RSpec because these
tests are inside the `spec/features` folder. Using `feature` re-adds a
`type: :feature` to these files, which will result in a conflict when we
upgrade to Rails 5.1's system tests.
Because of this change, we also need to change `background` to `before`
or else these tests will fail.
