Inline CsvFileFromPublicHost#csv_file
Inline CsvFileFromPublicHost#csv_file

This private method is only used in the constructor and so inlining it
into a local variable shouldn't cause any problems and I'm hoping it
will make it easier to do some refactoring that I'm planning.

alphagov/whitehall,alphagov/whitehall,alphagov/whitehall,alphagov/whitehall