Currently, the Download Raw Data action is available in the Windows Form Report Viewer. It is hard-coded there, and the download button appears when you hover over the data item.
The developer can cancel the action through the interactive action event handlers. However, the button persists even when the action is cancelled and doesn't do anything, which is misleading and confusing for the report readers.
Please let the developers disable the action/button, for example, through configuration in the viewer.