Stop inheriting from `StreamReaderProtocol`?

I was in the process of eyeballing the docs and fixing things when I came upon a `:ref:` that steadfastly refused to resolve:

:class:`asyncio.StreamReaderProtocol`

After hunting around, apparently that class was last documented in **Python 3.6**: https://docs.python.org/3.6/library/asyncio-stream.html#streamreaderprotocol

It's gone since **Python 3.7**, that's why the `:ref:` won't resolve.

Digging deeper, I found [`bpo-37639`](https://bugs.python.org/issue37639) with comment from @asvetlov (I'm assuming the same person, apologies if not):

> We are striving to remove it from public API step by step: documentation-deprecation-removal.
>
> If you really need the class -- please copy-paste the source lines into your project and use the copy on your own.

So, will we stop inheriting from that class and as suggested, just copy-and-paste the source lines?

I fear that one day things will blow up if this class's definition got removed and/or remade... which is why I'm adding the `[tech-debt]` label there.