Disabling some concurrency in widget tests

There has been frequent failures with CI, especially with OSX 10.7.
These seems to work ok in CI node when ran alone but CI is running
those in parallel with some other tests, and this is causing errors,
most likely due to lost focus.

Change-Id: Ic4151099c27a4b5d91778c9b13e88d2d661e8a0d
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

tests/auto/widgets/itemviews/qtableview/qtableview.pro

 CONFIG += testcase
-CONFIG += parallel_test
 TARGET = tst_qtableview
 QT += widgets widgets-private testlib
 QT += core-private gui-private

tests/auto/widgets/widgets/qstackedwidget/qstackedwidget.pro

@@ -3,7 +3,6 @@
 ############################################################
 
 CONFIG += testcase
-CONFIG += parallel_test
 TARGET = tst_qstackedwidget
 QT += widgets testlib
 SOURCES += tst_qstackedwidget.cpp