Stop sending FileError items to Kingfisher Process

[yolile]

open-contracting/kingfisher-process#366 (comment)

[yolile]

I think our options are:

1. As part of kingfisher_process_api2, stop sending FileErrors to Process, but instead log the error and return (I don't like this approach as it feels out of the scope of the extension)
2. Create a new extension only to log FileErrors (fewer changes to the existing code and logic)
3. Delete the FileError class and replace it with logging the error instead of yielding a FileError item (requires several changes to the code, I think)

@jpmckinney thoughts?

[jpmckinney]

3 is probably the best.