The function has always been documented as returning 0 or -1. It is in
fact `void`. Correct that. As part of the rearrangements we lose the
mention that `delete_tempfile()` might set `errno`. Because there is
no return value, the user can't really know whether it did anyway.
Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>