t7607: clean up stray untracked file

t7607: clean up stray untracked file

This file ends up conflicting with the test just after it
(causing the "git merge" to fail).  Neither test is to blame
for the bug, though. It looks like the merge in 1a9fe45
(Merge branch 'tr/merge-unborn-clobber', 2011-02-09) is what
caused the conflict.

We didn't notice because the follow-on test is already
marked as expect_failure (even though it has since been
fixed, and now succeeds once the untracked file is moved out
of the way).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>