Remove city-specific authentication tables post-unified login

[misaugstad]

Brief description of problem/feature

In #3712 we added unified login, but we kept the old authentication tables in each cities' schema in case anything went wrong. After the current system has been in place for a few weeks, we should be safe to delete those old tables (which will then be out of date anyway).

[misaugstad]

And when doing this, we should add the sidewalk_login schema to the search path for the db users (both in prod AND in dev env). Then we can remove the explicit references to the sidewalk_login that we have throughout the code.