Update tests Playground

[ysthakur]

Description

It looks like Playground and Director in nu-tests-support haven't gotten much love recently, so this PR is for updating them to work with newer Nushell versions.

• Director adds a --skip-plugins argument before running nu, but that doesn't exist anymore, so I removed it.
• Director also adds a --perf argument, which also doesn't exist anymore. I added --log-level info instead to get the performance output.
• It doesn't seem like anyone was using playground::matchers, and it used the hamcrest2 crate, which appears to be unmaintained, so I got rid of that (and the hamcrest2 dependency).
• Inside tests/fixtures/playground/config were two files in the old config format: default.toml and startup.toml. I removed those too.

User-Facing Changes

None, these changes only mess with tests.

Tests + Formatting

After Submitting

[rgwood]

Thank you!! Our test infrastructure has been a bit… “there be dragons” for a long time, really nice to see someone cleaning it up.