Add logging on assignment remove

What does this MR do and why?

Resolves: #424556

Adds info level log when a user add-on assignment is successfully removed.

How to set up and validate locally

All tests green.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.