This reverts commit 4c60a11d8f.
Reason for revert: Breaks QMainWindow::restoreState(). Dock widget is shown, even if restored into hidden state.
Change-Id: I9808de4e0fd48871c3b234ae9bbaf6c64c8e832d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>