refactor deleting users and fix bugs in delete

[shannonmhong]

refactor deleting users and fix bugs in delete

• admins can delete users from a user's profile

• when deleting a user, also deleting all references in other tables to that user
  (cascade on delete for many-to-many relationships don't work on prisma right now so just did it manually, an issue @ethanlee16 also mentioned in another PR)
  issue No way to cascade delete when the foreign key is non-nullable prisma/prisma#2057

How to Test/Use PR feature

1. from the "users/admin" page, click on any user
2. from the users profile, try deleting a user
3. should take you to the users dashboard after clicking "delete"

PR Checklist

Does your branch (check if true):
[X] work when you run yarn build?
[X] successfully run yarn:db-migrate up without yielding any errors?
[X] successfully run yarn prisma introspect without yielding any errors?
[X] successfully run yarn dev and support all changes that your branch intends to perform?

Screenshots

CC: @erinysong