Clean labelset image

Summary:
Remove dead code

This code seems to have never been implemented / working.

Remove unused "Concatenate"-function

Remove not-implemented "ChangeLayerProcessing"-function

Remove commented code

Remove layer-parameter from erase-function

The layer-paramter is passed on to the "EraseLabelProcessing"-function,
where the parameter is finally commented and not used.

Use consistent parameter names

Test Plan: manual inspection

Reviewers: floca, kislinsk, O1 MITK Reviewer Group I

Reviewed By: floca, O1 MITK Reviewer Group I

Subscribers: kalali, kislinsk, floca

Maniphest Tasks: T28524

Differential Revision: https://phabricator.mitk.org/D642