Users: Deleting a user should automatically unassign them from tasks

[martastain]

Story

To reproduce

Steps to reproduce the behavior:

• Create a user.
• Assign that user some tasks.
• Delete that user.
• Create them again with the same name.
• They are still assigned the same tasks

Expected behavior

This is up to discussion. It may be considered a bug or a feature. Generally, it is discouraged to delete users when they are active on a project. User should rather be deactivated so all related activities still points to an existing user DB record.