awk: Fix the tests

I'd forgotten that we have to adjust the stderr tests from
upstream. Remove the OK files. Also remove system-status.*. These
restore the fixes I made in 517e52b6c21c which were lost when I imported
the last version of awk.

Also, force LANG to be C.UTF-8 when testing to ensure that stray lang
settings don't fail tests.

Sponsored by: Netflix

(cherry picked from commit ba7b7f94c239ce43343d7af403734fdc941b7664)