Migration to remove unused contact columns

Contact details are now translatable, so all data (even for the English
locale) are kept in a separate table.

Also fix up a few test failures caused by the fields being missing from
the contacts table.
Merge pull request #1018 from alphagov/remove-unused-contact-columns

https://www.pivotaltracker.com/story/show/53558977

Migration to remove unused contact columns