Deprecation of db access in JupyterHub is coming, need to address

[rcthomas]

The JupyterHub 3.0.0 beta is out. Access to the db attribute on Authenticators and Spawners triggers a warning there:

[W 2022-08-12 16:09:44.804 JupyterHub spawner:170]
    The shared database session at Spawner.db is deprecated, and will be removed.
    Please manage your own database and connections.
    Contact JupyterHub at https://github.com/jupyterhub/jupyterhub/issues/3700
    if you have questions or ideas about direct database needs for your Spawner.

Here's a link to the issue for more info: jupyterhub/jupyterhub#3700

In wrapspawner the db attribute is accessed when creating a child spawner. If this attribute goes away, it doesn't need to be copied, so I think this is not that big a deal to address here.