Remove unused SlicesCoordinator

Summary: Remove SlicesCoordinator-class from MITK

Test Plan: no build errors in CI

Reviewers: kislinsk, O1 MITK Reviewer Group I

Reviewed By: kislinsk, O1 MITK Reviewer Group I

Subscribers: kislinsk, kalali

Maniphest Tasks: T29222

Differential Revision: https://phabricator.mitk.org/D682