Move pending migrations to db/migrate/

All of the changes these relate to have been live for at least six weeks
and there haven't been any problems.

Remove deprecated_columns calls for the dropped columns
Remove old edition_world_location columns

Also drop the edition_world_location_image_data table.
Merge pull request #1186 from alphagov/run-pending-migrations

Move pending migrations to db/migrate/

All of the changes these relate to have been live for at least six weeks and there haven't been any problems.

I've left the supporting pages migration as pending because there are a few tests that use the old table and we've had to use it to retrieve old data a couple of times.