Can't remove resource file/URL via the UI widget

[grugnog]

Describe the bug

The UI has a "Remove" button, but after using it and saving the dataset (without replacing) the previous file/URL is retained. It's possible to work around this if you have a file/URL ready to replace with, or by going in and editing the distribution node directly.

I expect this is an issue with the file/URL widget.

Steps To Reproduce

• Create a dataset and add a file/URL
• Edit the dataset
• Click the "Remove" button on the file/URL
• Save the dataset
• Edit the dataset
• The original file/URL is still there

Expected behavior

• The original file/URL is removed