User mentions are not disabled when a licensed user is changed to a Guest user

Issue Summary

User mentions are not disabled when a licensed user is changed to a Guest user

This is reproducible: (yes) 

Steps to Reproduce

1. Onboard a user as a licensed user
2. Remove them from all the groups and enable the account as a Guest user.
3. Navigate to any page and attempt to @mention users

Expected Results

As per documentation Guest users should not be able to @mention users.

Actual Results

Guest users are able to @mention users.

Workaround

Currently, there is no known workaround for this behaviour. A workaround will be added here when available