Remove legacy azure nbmanager

This deletes the code for the azure notebook manager, which no longer works with the current notebook management scheme (files, not UUIDs)

I started [migrating bookstore to use libcloud](https://github.com/rgbkrk/bookstore/tree/libcloud) to make the cloud based storage of notebooks abstracted across providers. First step there is getting it to work with the old 1.x releases, then getting it to work with 2.x.