Unbreak the build

[odersky]

For some reason, BestEffortTastyWriter does not compile since PlainFile does not have a delete method, only File does.

[odersky]

I wonder: Why did the original failing code get through the CI?

[odersky]

I see now it's already handled in #20355. On the other hand, maybe the fix here is preferable. I see that lots of classes have unimplemented delete methods. So maybe it's not such a good idea to add it, after all?

[odersky]

In any case, we should merge either this PR or #20355. I leave it to you to decide which.

[jchyb]

It was an old PR, which had a passing CI run on top of old main without the changes. I didn't realize that when I was asked to review it earlier today. I prefer this fix, but I wanted to have the main fixed as soon as possible so I tried to revert after noticing. Seems like both CIs got stuck on test_windows, but I believe those errors to be spurious. I will try to restart the failed tasks, and I will merge the PR that will have a successful run (but preferably this one).

[odersky]

It was an old PR, which had a passing CI run on top of old main without the changes.

I see, that explains it. Maybe we should have a recommendation that old PRs are re-tested before merge. On the other hand, that would have added to the crazy build load we had today.