t5317: use ! grep to check for no matching lines

t5317: use ! grep to check for no matching lines

Several times in t5317, we would use `wc -l` to ensure that a grep
result is empty. However, grep already has a way to do that... Its
return code! Use `! grep` in the cases where we are ensuring that there
are no matching lines.

While at it, drop unnecessary invocations of `awk` and `sort` in each
affected test since those commands do not influence the outcome. It's
not clear why that extra work was being done in the first place, and the
code's history doesn't shed any light on the matter since these tests
were simply born this way[1], likely due to copy-paste programming. The
unnecessary work wasn't noticed even when the code was later touched for
various cleanups[2][3].

[1]: 9535ce7337 (pack-objects: add list-objects filtering, 2017-11-21)
[2]: bdbc17e86a (tests: standardize pipe placement, 2018-10-05)
[3]: 61de0ff695 (tests: don't swallow Git errors upstream of pipes, 2018-10-05)

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>