t4018: drop "debugging" cat from hunk-header tests

t4018: drop "debugging" cat from hunk-header tests

We run a series of hunk-header tests in a loop, and each one does this:

  test_when_finished 'cat actual' &&      # for debugging only

This is pretty pointless. When the test succeeds, we waste time running
a useless cat process. If you're debugging a failure with "-i", then we
won't run the when-finished part at all. So it helps only if you're
running with something like "--verbose-log".

Since we expect the tests to succeed most of the time, a better way to
do this would be a helper that checks the output and dumps "actual" only
when it fails. But it's probably not even worth the effort, as anyone
debugging a failure could just run with "-i" and investigate the
"actual" file themselves.

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