Dialogs examples: remove QLayout::SetNoConstraint

These constraints were adjusted in qt4 commit 3abaecc in order to make
the dialogs fit Symbian/Maemo screens. These are not mobile oriented
examples and it breaks resizing behavior on desktop so badly, that
we will simply revert the constraint changes to make the dialogs
respect their minimum sizes.

Task-number: QTBUG-31351
Change-Id: Ibf358ddedadf05614ef7a66b6a98fe5d7073996f
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Caroline Chao <caroline.chao@digia.com>