When deprecated classes are still around for a long time it is a valid base assumption that the reason is just that they were either forgotten since they weren't used or seen for a long time, or that it is surprisingly difficult to actually get rid of them since there's no real replacement for example but they are still in heavy use. The latter reason is something seen rather often in the core unfortunately.

Another deprecated class: Just found out there is a QmitkOtsuAction inside the org.mitk.gui.qt.segmentation, which is not listed in the files.cmake-file. It was deprecated in rMITKc9037280cb9f: made otsu action deprecated and removed it from DataManager and it's not used anywhere anymore.

When I look for occurrences of mitkOverwriteSliceImageFilter, I see a description inside ApplyDiffImageOperation and DiffImageApplier that says

At the moment, ApplyDiffImageOperations are only created by OverwriteSliceImageFilter.

or

Instances of this class are created e.g. by OverwriteSliceImageFilter.

However, the mentioned mitkOverwriteSliceImageFilter is nowhere used and was replaced by mitkVtkImageOverwrite. I found occurrences of ApplyDiffImageOperation and DiffImageApplier inside QmitkSlicesInterpolator.cpp, so I changed the description accordingly.

A first differential was created. There is another class QmitkThresholdAction that is not included anywhere and has not been touched for a long time. I don't see any reason for keeping this class. So I updated the differential with the removal of this class as well.