Do not set the interaction scheme

Summary:
Do not set the default event config for the interaction scheme

This abstract class does not need to define a default event config.
Any subclass of this class needs to make sure that a valid
event config is loaded elsewhere (e.g. by using the InteractionSchemeSwitcher,
see also QmitkAbstractMultiWidget::SetInteractionScheme).

Test Plan:
manual testing:

• open StdMultiWidget / MxNMultiWidget
• change interaction modes inside the preference pages
• see how all interaction modes are correctly loaded

Reviewers: s434n, O3 MITK Reviewer Group II

Reviewed By: s434n, O3 MITK Reviewer Group II

Subscribers: kalali, s434n

Maniphest Tasks: T24358

Differential Revision: https://phabricator.mitk.org/D551