Is it safe to mass delete users from the database directly We have a client site that has been getting a lot of spam registrations. We're turning on purgePendingUsersDuration to help deal  with some of these automatically, but I was planning to go into the database to delete a bunch in bulk directly (since there are almost 200 of them)

Is it safe to delete them just from craft_users and craft_usergroups_users tables? Are there other places I should watch out for?
If you want to delete users (or any other elements in Craft) directly from the database, the place to do that is the elements table. Delete the row(s) from there, and all the elements’ rows in the other tables will go away automatically.