t3419: drop EXPENSIVE tests

t3419: drop EXPENSIVE tests

When t3419 was originally written, it was designed to run a smaller test
for correctness, and then the same test with a larger number of patches
for performance. But it seems unlikely the latter was helping us:

 - it was marked with EXPENSIVE, so hardly anybody ran it anyway

 - there's no indication that it was more likely to find bugs than the
   smaller case (the commit message isn't very helpful, but the original
   cover letter describes it as: "The first patch adds correctness and
   (optional) performance tests".

 - the timing results are shown only via test_debug(). So also not run
   unless the user says "-d", and then not provided in any
   machine-readable form.

If we're interested in performance regressions, a script in t/perf would
be more appropriate. I didn't add one here, because it's not at all
clear to me that what the script is timing is even all that interesting.

Let's simplify the script by dropping the EXPENSIVE run. That in turn
lets us drop the do_tests() wrapper, which lets us consistently use
single-quotes for our test snippets. And we can drop the useless
test_debug() timings, as well as their run() helper. And finally, while
we're here, we can replace the count() helper with the standard
test_seq().

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