tst_QSqlQuery: remove tests commented out a long time ago

Remove some code which was commented out with 'NOT_READY_YET' since the
initial Qt5 import. Since the mentioned bug reports are no longer
available remove this code.

Change-Id: I98686e53d85619f01d16105d147eba79b557a104
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>