do not set default switches in Test::Harness; not even -w

This commit is meant to address https://github.com/Perl-Toolchain-Gang/Test-Harness/wiki/TAP::Harness-and--the-w-flag

Rather than change Test::Harness, the compatibility layer for TAP::Harness, this changes the actual thing we have been complaining about: `make test` turning on -w globally.