Correctly disconnect the time navigation controller

Summary:
Disconnect time navigation controller

If a render window widget is removed, the time navigation controller
has to be disconnected, otherwise the non-existent render window
still observes GeometryTimeEvents.

Test Plan:
manual testing

1. open MITK workbench, load a dataset
2. close the standard display, open the mxn display
3. use the layout button to create more render windows
4. use the layout button again to create less render windows
5. reinit the loaded dataset
6. without this fix MITK will crash

Reviewers: s434n, O3 MITK Reviewer Group II

Reviewed By: s434n, O3 MITK Reviewer Group II

Subscribers: floca, kalali, s434n

Maniphest Tasks: T29240

Differential Revision: https://phabricator.mitk.org/D692