Remove cookies and passwords and hub (3)

[DonJayamanne]

Part of #12832

• Remove code for Jupyter hub (it has not worked for 2 years, and its completely broken)
• If a 3rd party is providing a Jupyter server, the expectation is that will give the necessary auth headers
• hence the feature of supporting password protected Jupyter Server uris is very specific to user provided uris
  • That's not a generic feature, its a standalone feature
  • Thus cookies, passwords, etc all go out of generic jupyter/kernel code/layers.
  • Now we ONLY handle headers, previously we would inject cookies, xsrf, headers, base urls, baseToken in number of places and different ways, all very complicated and unnecessary. All replaced with headers