Remove DrupalStandardsListenerTrait - it's broken, does not prevent errors, blocks better tooling

Given that this is broken, phpstan-phpunit can do a better job, and we would have to rewrite or remove this anyway for PHPUnit 10, to me this is OK to commit now and unblock the introduction of phpstan-phpunit.

I ummed and ahhed about deprecating - but as it is @internal and broken I think removal is best. I also ummed and ahhed about a change record but decided that that was not necessary for the same reason. Also there are no contrib usages - see https://git.drupalcode.org/search?group_id=2&repository_ref=&scope=blobs...

Committed 4e74e716c5 and pushed to 10.1.x. Thanks!

Thanks everyone for getting this ball roiling again!

mondrake → closed merge request !3727

Automatically closed - issue fixed for 2 weeks with no activity.