filesystemmodel: Notify correct position removed in remove_file()

Merged Corey Berla requested to merge wip/corey/filesystemmodel into main

32247bc5 made several changes to account for the fact that we no longer have a NULL editable at the beginning of the list model. The commit mistakenly left out one change in remove_file(), which causes the wrong file to be removed.

This should also be cherrypicked into 4.10

cc: @matthiasc

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