Remove Tornado monkeypatch

[takluyver]

PR #948 monkeypatched Tornado versions <= 2.1.1, so they work with Chrome 16. This is just to remind us to remove the monkeypatch from frontend/html/notebook/handlers.py once we're happy that future releases of Tornado are sufficiently widespread.

[damianavila]

Since we are using tornado 3.1.0 as a requirement and AFAIK the monkeypatch was removed, I think we can close this issue.

[takluyver]

Yep, I agree that this is done. Thanks for the reminder.