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

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:

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

[Penwy]

Can confirm fix on ubuntu 24.04