dgit: unrepres. changes: Tolerate deletion of executable files

dgit: unrepres. changes: Tolerate deletion of executable files

We don't care what the old mode was; if we tell dpkg-source to record
the deletion it can do so.

But we do care that it was a file.  Experimentally, dpkg-source on
stretch ignores attempts to delete symlinks.

The removal of the check for $newmode has no functional change,
because in this context we know that $newmode is all 0s.  If it
wasn't, we would have been in "both old and new files exist", above.
So that limb of the test will never match and should be removed.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>