No report designer won't allow you to remove files that have been added to the report. You would need to redesign the report. In the future use Tools, Available fields to determine which tables you need to get the information you need on the report.  You could set data file selection within the report design (Design, Data File selection) so it doesn't keep prompting, but I would still recommend redesigning from scratch so the unused tables aren't included in the design as there can be other issues with the report when tables that aren't being used are included in the design.

That's what I always thought. I was just hoping I had overlooked the option to remove files.

I know I can define default file selection in the design and disable the prompt asking the users to pick but would the report templates runs slower if I leave those file linkages?