An icon for removing the file from the list would be nice. This is currently only possible via the context menu on the file entry. When the file is selected and I press the DELETE key, the entire entry will be removed (the confirmation dialog leaves it open whether it is about the file or the entry).
Was present in JabRef 2.10, is not in JabRef version 4.0 beta2 on Ubuntu 16.04.
BTW: For links, the remove menu item is grey and therefore it does not seem to be possible to remove links from the file list.