T30422-Remove_erase_tool_background_click

Summary:
BREAKING: Removed background click feature from EraseRegionTool Why: Testers were regulary supprised/irritated by the feature How to adapt: Use the "clear label" option in the context menue of the label inspector.

+ Fixed 30422

Test Plan: code review; UI (feature is removed from tool)

Reviewers: O1 MITK Reviewer Group I, kislinsk

Reviewed By: O1 MITK Reviewer Group I, kislinsk

Differential Revision: https://phabricator.mitk.org/D950