feat: Remove OIDC and SSO support

Existing SSO accounts have no local password, so the migration
deactivates them before dropping is_sso_user and the
identity_provider_user table.

server/db/seeds/default.js

@@ -8,7 +8,6 @@ const bcrypt = require('bcrypt');
 const buildUserData = () => {
   const data = {
     role: 'admin',
-    isSsoUser: false,
     isDeactivated: false,
   };