Switch to new user tables

[dgitis]

We already support the new user tables but have some issues with tests as we have two sets of user tables but disabling one set causes the other set's to fail.

The existing new user tables implementation needs to be updated to support multi-site. There's a draft PR that is close but I'm pretty sure I found a bug that I didn't fix in that draft.

We also need to deprecate the old user tables and then we want to delete the new user tables from the next 6.x release as 6.x will support old implementations that pre-date Google's introduction of new tables and fields while 7.x will drop the old mechanisms and only support new implementations that post-date the new tables and fields.

[bhujbal-aarya]

please assign me this issue

[dgitis]

Thanks for your help @bhujbal-aarya .

For this, we just need to update the PR I created that includes the new user tables and multi-site (I remember there was a bug or logic error in my code, but not what it was) to work and delete all of the legacy user tables.

There's probably some other wrangling. The latest version of the package includes single-site user tables and that PR has mostly working code for multi-site.