Re-enable tests tst_qgraphicsproxywidget, tst_qgraphicswidget.

Task-number: QTBUG-25294
Task-number: QTBUG-20778

Change-Id: I6b6e19e812d5527465c6162e2df2e4807cf160da
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>