1579 cleanup

> The tests for this do expect on puts.

I consider such a mock expectation to be problematic...I commented on it there.

Anyhow, I meant to have a spec that configures `raise_errors_for_deprecation_warnings!` (to have it use a `RaiseErrorStream` instance), and then trigger this warning and show that it does the right thing.

That said, this is 2.99 so I care _much_ less than for the master branch so if you think that's overkill we can skip that.