do not apply asyncio patch for tornado >=6.1

[bollwyvl]

Tornado 6.1 now no longer requires the asyncio patch on windows for python >=3.8. 🎉

On jupyter-server/jupyter_server#339, we went with a hard cut to require 6.1, and remove the patch, but this PR applies the lighter touch from ipython/ipykernel#564 of just not applying the patch.

Fixing this is good, as the error manifests itself as unkillable python hang on windows, timing out CI.

[bollwyvl]

Ha, thanks @minrk! How you doing?

I made some progress on #5909 so this could be exercised a little harder (especially getting the selenium tests to run on windows under a representative deployment) but looks like nobody's ever done it before, so it's slow going. Will be doing some more looking!

[bollwyvl]

Also, incidentally: can you think of any other places we had to do this stuff? I think i hit most of them...

[minrk]

can you think of any other places we had to do this stuff?

I did a search and it looks like:

• ipykernel
• notebook
• qtconsole
• jupyterhub
• nbconvert
• nbdime

[minrk]

How you doing?

I'm okay! Super busy and spread a little thin, but trying to keep up. How are you? :)

[bollwyvl]

Same... it'll be great when all the stuff that's in the air lands, but it does seem like a lot right now!

[minrk]

Looking back at tornado docs, I think we should still be using the selector loop all the time. Performance will be better, as ~everything we do is built add/remove_reader, which are slower when proactor is used do to the extra thread.