SWORD: stop calling DeleteDataFileCommand

[pdurbin]

@scolapasta indicated that the SWORD code needs to be modified to not call DeleteDataFileCommand. It should instead call UpdateDatasetCommand.

[pdurbin]

I made the change in b62334a which @scolapasta might want to review.

Passing to QA. I only tested deleting files from unpublished datasets, which seems to work fine. Also, #1784 could go through QA now perhaps since it's related.