Assistant: prevent the main window from jumping during startup

Remove the 6 year old hack which causes an early show of the main window.

Change-Id: I1c8d782b3ecd7278068b5a21d34fef937585f25d
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>