Cleanup the drilldown example:
- use icons with the current style
- remove unneeded QOverload<>
- remove some empty lines which don't look good in the documentation
- use Q_SLOTS/Q_SIGNALS instead slots/signals
Fixes: QTBUG-113696
Change-Id: I62476a8989c0abd1f424d1425cb05489491e2153
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
fa045a3ce7