Name conflicts with new ldap users when system users exist even if system users are in deleted state

[reedv]

Description
A clear and concise description of what the bug is.
The ldap extension raises naming conflict errors on login attempt if the CKAN system ever had a local user with the same name as the LDAP user, even if such a system user has since been deleted from CKAN.

There is a username conflict. Please inform the site administrator.

(The issue appears to be that the system user will still exist in the backend CKAN DB's user table with value state=deleted).

Ran into this problem when trying to migrate existing CKAN system from local users to LDAP users (where the old, deleted local user were using their regular LDAP/AD based names).

Expected Behaviour
What you expected to happen instead.
When signing into CKAN as an LDAP user. If no other user of the same name exists on the CKAN system, they should be able to sign in.

To Reproduce
Steps to reproduce the bug.

1. Set ckanext.ldap.ckan_fallback = True in the ckan.ini file
2. Create a system user w/ name xxxxxx
3. As a CKAN sysadmin, delete that system user xxxxxx from you ckan site https://myckan.net/user/ list
4. Attempt to sign in as an LDAP user of same username xxxxxx

Error Log
Paste any relevant error logs below:

<error log here>

Screenshots
Add screenshots to illustrate the bug if you want.

Your Setup

• CKAN version: 2.9.1
• Commit/version of this repo: Installed from package
• Browser (if relevant): [e.g. chrome, safari]

Anything Else?
...

[ghost]

Any news about this?