The test did "reset --hard" (where the HEAD commit has an empty
blob at path "empty") followed by "> empty", expecting that
the index does not notice the file _changed_ since git wrote
it out upon "reset" if the redirection is done quickly enough.

There was no need to do the emptying, and it gave a wrong result
if "reset --hard" happened on time T and then ">empty" happened on
the next second T+1.  This fixes it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>