Every reg-test now runs without any warning, so let's acivate -dW by
default so the new ones will inheritate the option.
This patch reverts 9d511b3c ("REGTESTS: enable -dW on almost all tests
to fail on warnings") and adds -dW in the default HAPROXY_ARGS of
scripts/run-regtests.sh instead.
Now that warnings were almost all removed, let's enable zero-warning
via -dW. All tests were adjusted, but two:
- mcli/mcli_start_progs.vtc:
the programs section currently cannot be silenced
- stats/stats-file.vtc:
the warning comes from the stats file itself on comment lines.
All other ones are now OK.
