Resolve "ParamUpmix Cleanup"

• Related issues: #891 (closed)
• Requested reviewers:

Reason why this change is needed

Cleanup for clarity.

Description of the change

Remove unused code.

Affected operating points

Produced bitstream is BE compared to previous state. Produced output is BE to previous state.

Test Link: https://forge.3gpp.org/rep/ivas-codec-pc/ivas-codec/-/pipelines/26244