[bug] Message Erasure Type `Keep Messages And User Name` not work as expected

Description:

In Admin UI - Message we have Message Erasure Type option.
Default is Delete All Messages
But if you set Keep Messages And User Name - you get same behavior and Delete All Messages set - all users messages are deleted.

Steps to reproduce:

1. Set Keep Messages And User Name value in Admin UI - Message
2. Delete user that had messages in DM and other chats
3. No messages of deleted user remain

Expected behavior:

User account should be deleted, but messages in chat history should remain and be authored as deleted user (when that user was on server, for example UserA @usera)

Actual behavior:

Server Setup Information:

• Version of Rocket.Chat Server: 4.2.0
• Operating System: CentOS7
• Deployment Method: docker
• Number of Running Instances: 10
• DB Replicaset Oplog: Enabled
• NodeJS Version: 12.22.1
• MongoDB Version: 4.2.17

Client Setup Information

• Desktop App or Browser Version: Chrome 96
• Operating System: Windows 10

Additional context

Tested on 3.18.3 with same result

Third option look like work fine

Relevant logs:

Start at the Admin UI Message Erasure Type setting and follow the user deletion flow described in the reproduction steps. Reproduce the Keep Messages And User Name case, compare it with Delete All Messages and the third option, and consider the issue done when deleted users' messages remain attributed to the deleted user while the account is removed.