They are needed in the timeline view.
The change in qtcreator-project.qdocconf makes sure
that qdoc still finds the referenced icons.

Change-Id: I812fba8e57d06d93efc00c295467c83c08cd1784
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>