Duplicate Manager needs better documentation and messages for deletion of duplicates

Is your feature request related to a problem? Please describe.
The manual for darktable does not mention what happens when you delete a duplicate (using the "x" in the upper right hand corner of an image in the duplicate manager). So it was unclear to me what would happen when I did that until I experimented with it.

Furthermore the message that the duplicate manager uses sounds like it will be deleting the RAW file from the disk, but that only affects the duplicate. It would be better if the message made it clear what was actually being deleted (just the .xmp file for the duplicate, I believe).

Describe the solution you'd like
The documentation should describe what happens when a duplicate is deleted and the message attached to the confirmation should be clearer about what is being deleted.

I also expected the duplicate manager to be available in the lightable view, but it isn't.

Alternatives
One could copy the relevant files first and then try out deletion in the duplicate manager to see what happens.

Start with the duplicate manager entry point and the manual section covering duplicate deletion. Confirm what the upper-right “x” deletes and review the confirmation message’s current wording, then update the documentation and message so the affected duplicate and file are explicit. Check whether lighttable availability is part of this issue or a separate request.