Re-enable tests dependent on QStandardItemModel.

These were disabled when QtWidgets was not available, but that is no
longer necessary following QStandardItemModel being moved to QtGui.

Change-Id: I7ed133d9fd5ae6daa5ed9df180f7745fc3f368b1
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: Damian Jansen <damian.jansen@nokia.com>