Downgrading license from Premium to Starter Keeps User as Auditor enabled which prevents LDAP login
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### Summary
Given a GitLab instance with a **Premium** license with a User with **Auditor** access - LDAP login is **successful**.
Downgrade license to **Starter** - LDAP login is **unsuccessful**.
### Steps to reproduce
1. GitLab **Premium** license
1. User with Access level **Auditor**
1. LDAP enabled
1. Downgrade license to **Starter**
### Example Project
### What is the current *bug* behavior?
User is presented with alert message - `Access denied for your LDAP account`
### What is the expected *correct* behavior?
Successful login.
### Relevant logs and/or screenshots
From GitLab `admin`, when impersonating the User we see
```
{"severity":"INFO","time":"2020-08-11T23:24:45.551Z","correlation_id":"rsDWJiXOkfhn","message":"(LDAP) Error saving user ... [\"Auditor user cannot be created without the \\\"GitLab_Auditor_User\\\" addon\"]"}
```
### Output of checks
(If you are reporting a bug on GitLab.com, write: This bug happens on GitLab.com)
#### Results of GitLab environment info
Detected in GitLab version `13.2.2` via customer [ZD](https://gitlab.zendesk.com/agent/tickets/167918) (internal use only)
### Possible fixes
For each user affected, via the admin UI, change access level from Regular to Admin, then back to Regukar.
issue