Qt Designer/widgetdatabase: Remove unused member variable m_form.

Change-Id: I68ed51365a6341b2d537fe4eaf22f9eae1432483
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>
Assistant: Remove InstallDialog.

Task-number: QTBUG-32390
Change-Id: I160b1a15198a51869716b339bb356eb0740f5adc
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>
Merge remote-tracking branch 'origin/stable' into dev

Change-Id: I5368a3b3212af59ac5b95bc56c667b0d3392078a