frontend: Remove audio source from audio mixer on remove signal

[exeldro]

Description

Remove audio source from audio mixer on remove signal

Motivation and Context

deactivate signal is not provided for removed source so the remove signal should have same effect
Fixes #12919
This change is not needed if #12735 is merged

How Has This Been Tested?

On windows by using steps from #12919

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[Penwy]

Can confirm fix on ubuntu 24.04